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Trichoblastomas are epithelial tumors consisting mostly of follicular germinative cells. Depending upon the investigator and the histologic criteria utilized, these tumors may be more common than believed. There are rare cases of malignant degeneration.


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Trichoblastoma is the most common neoplasm developed in nevus sebaceus of Jadassohn.

Jaqueti G, Requena L, Sáchez Yus E.

Am J Dermatopathol 2000 Apr;22(2):108-18 Abstract quote

Nevus sebaceus of Jadassohn is a hamartoma that combines epidermal, follicular, sebaceous, and apocrine gland abnormalities. Classically, several types of cutaneous neoplasms have been associated with this hamartoma, with basal cell carcinoma being the most frequently described malignancy.

We studied a series of 155 examples of nevus sebaceus of Jadassohn with clinicopathologic correlation.

Several histopathologic changes related to the age of the patients were found. In our series, we could not identify any cases of authentic basal cell carcinoma. In contrast, several examples of primitive follicular induction and of trichoblastomas were seen. Other cutaneous hamartomas, hyperplasias, and neoplasms found in our series of nevus sebaceus of Jadassohn included syringocystadenoma papilliferum, sebomatricoma, apocrine gland cyst, poroma, different histopathologic variants of warts (classic warts, tricholemmoma, and desmoplastic tricholemmoma), primitive follicular induction, and ductal induction. In our series, no examples of malignant neoplasms were identified.

On the basis of these findings, the classically recommended treatment for this hamartoma, which consists of early excision to prevent the development of malignancy, seems to be inappropriate.

PTCH mutations are not mainly involved in the pathogenesis of sporadic trichoblastomas.

Department of Dermatology, University of Regensburg, 93042 Regensburg, Germany.

Hum Pathol. 2007 Oct;38(10):1496-500 Abstract quote

Trichoblastomas are rare, benign tumors of the appendix in human skin. The histopathology comprises elements of basal cell carcinoma and trichoepithelioma with a variable degree of follicular differentiation. Both basal cell carcinoma and trichoepithelioma reveal alterations of PTCH, the human homolog of the Drosophila segment polarity patched gene. Furthermore, heterozygous PTCH knockout mice develop trichoblastoma-like tumors. This suggests an involvement of the PTCH gene in the pathogenesis of human trichoblastomas. However, trichoblastomas arising in nevus sebaceus did not show loss of heterozygosity at the PTCH locus (9q22.3) in a previous study. Sequencing of the PTCH gene and analysis of sporadic human trichoblastomas have not been performed yet.

We therefore screened 10 sporadic trichoblastomas and 1 trichoblastoma arising within a nevus sebaceus for PTCH mutations. After microdissection of the tumors, single-strand conformational polymorphism (SSCP)/heteroduplex analysis of exons 2 to 23 of PTCH was performed, and polymerase chain reaction products with aberrant band patterns were sequenced. One trichoblastoma revealed a silent mutation at codon 562 in exon 12. Another trichoblastoma showed a somatic C > T single nucleotide substitution at codon 1,315 (exon 23), which was not present in corresponding normal epidermis. This mutation at codon 1,315 represents an already described PTCH germline polymorphism and results in a heterozygous Pro to Leu substitution in the tumor. The Pro/Leu polymorphism in germline is associated with a higher risk for breast cancer, but a potential contribution to the tumorigenesis of trichoblastoma is unknown. We detected no classical PTCH mutations in the investigated trichoblastomas.

Our results indicate that PTCH mutations are not mainly involved in the pathogenesis of sporadic trichoblastomas, in contrast to basal cell carcinomas and trichoepitheliomas. The genetic basis of this rare appendageal tumor remains elusive.



Nodular desmoplastic variant of trichoblastoma.

Chan JK, Ng CS, Tsang WY.

Institute of Pathology, Queen Elizabeth Hospital, Kowloon, Hong Kong.

Am J Surg Pathol 1994 May;18(5):495-500 Abstract quote

A case of an unusual, previously unreported, nodular desmoplastic variant of trichoblastoma (hair germ neoplasm) in the scalp of a 65-year-old woman is reported.

Four discrete nodules were present in close proximity at presentation. Another nodule developed in the same vicinity 3 1/2 years after excision, and there was no further recurrence 2 1/2 years later. The tumors were located in the dermis, made up of cords of primitive hair germ-like structures radiating down from discrete hyalinized nodules located in the superficial dermis. There were small foci of keratinization or mucoid change within the epithelial islands. Toward the deep portion of the tumor, the epithelial cells became spindly and grew in a more dispersed pattern, within a desmoplastic stroma. There was also infiltration of the epineurium of the cutaneous nerves and arector pili muscle.

This uncommon benign neoplasm of hair germ merits wider recognition; in particular, this desmoplastic variant may mimic invasive carcinoma, morphea-type basal cell carcinoma, desmoplastic trichoepithelioma, and desmoplastic trichilemmoma. Distinguishing this variant from the former two possibilities is particularly important in order to avoid unduly aggressive treatment.

Giant trichoblastoma on the scalp.

Requena L, Barat A.

Department of Dermatology, Fundacion Jimenez Diaz, Universidad Autonoma, Madrid, Spain.

Am J Dermatopathol 1993 Oct;15(5):497-502 Abstract quote

We describe a case of giant trichoblastoma that had been present for many years on the scalp of a 69-year-old man.

The specimen was examined histopathologically, immunohistochemically, and ultrastructurally. Histopathologic examination showed that neoplastic cells were arranged in different patterns from area to area, including rippled, adenoid, and palisading patterns. In some areas of the neoplasm, foci of sebaceous differentiation were also present. The ultrastructural characteristics of neoplastic cells support the notion that trichoblastomas are neoplasms composed mostly of follicular germinative cells.

Vulvar Trichogenic Tumors: A Comparative Study With Vulvar Basal Cell Carcinoma.

Regauer S, Nogales FF.

From the *Institute of Pathology, Medical University of Graz, Graz, Austria; and the daggerDepartment of Pathology, University of Granada, Granada, Spain.
Am J Surg Pathol. 2005 Apr;29(4):479-484. Abstract quote  

Trichogenic tumors are very rare in genital skin and often cause diagnostic problems because they are mitotically active and they share some histologic features with basal cell carcinomas (BCCs).

We present the clinical and histologic features of 16 vulvar trichogenic tumors (6 plaque-like, 10 nodular; average age, 65 years) in comparison with 16 BCCs (11 plaque-like, 5 nodular; average age, 78 years). All trichogenic tumors, except 1 case with HSV infection, were nonulcerated tumors. Superficial plaque-like trichogenic tumors featured basal keratinocyte proliferations with peripheral nuclear palisading but no clefting at the epithelial-stromal interface. Nodular trichogenic tumors consisted of solid lobules of squamous cells and anastomosing cords and reticulations of follicular germinative cells with mitoses and apoptosis. Large pink cells with trichohyaline granules and melanocytes resembling the inner hair sheath, and clear cells resembling the outer root sheath were common. Most cysts were keratinized, but some fluid-filled cysts showed apocrine and sebaceous differentiation. The well-defined mesenchymal component of trichogenic tumors was pale and mucinous, and contained fibrocytes and fibrillary collagen bundles.

All BCCs showed surface ulcerations and clefting at the stromal-epithelial interface. BCCs showed no trichogenic differentiation and lacked an organized mesenchymal tumor component. The tumor stroma of BCCs was paucicellular, mucinous, or granulation tissue-like with an inflammatory infiltrate.


General Five main pattern which also may be a combination of two or more patterns within one tumor
Large nodular
Small nodular
(Malignant trichoblastoma)
High-grade trichoblastic carcinoma arising in trichoblastoma: a rare adnexal neoplasm often showing metastatic spread.

Schulz T, Proske S, Hartschuh W, Kurzen H, Paul E, Wunsch PH.

Institute of Pathology, Ansbach, Germany.

Am J Dermatopathol. 2005 Feb;27(1):9-16. Abstract quote  

It has been debated whether malignant transformation of trichoblastoma occurs. The concept was recently forwarded that basal cell carcinoma is as a malignant neoplasm of follicular germinative cells and should be named trichoblastic carcinoma to show its relationship to trichoblastoma. Almost all basal cell carcinomas are low-grade malignant neoplasms and develop metastases only very rarely, and if so, only after very long duration and untreated growth. Only rare basal cell carcinomas arise in trichoblastomas. Up to now there have only been two reports of high-grade trichoblastic carcinoma arising in trichoblastoma, showing systemic metastatic spread and death.

We add two further cases of trichoblastic carcinoma with anaplastic nuclei, arising in trichoblastoma. One of the tumors arose in a small nodular trichoblastoma on the right forearm of an 84-year-old male patient. The other one was a trichoblastic carcinoma at the base of a trichoepithelioma on the right thigh of an 87-year-old woman with Brooke-Spiegler syndrome.

Our cases emphasize that high-grade trichoblastic carcinoma develops via malignant transformation of trichoblastoma, and is very rare.
Low-grade trichoblastic carcinosarcoma of the skin.

Kazakov DV, Kempf W, Michal M.

Sikl's Department of Pathology, Charles University, Medical Faculty Hospital, Pilsen, Czech Republic.
Am J Dermatopathol. 2004 Aug;26(4):304-9. Abstract quote  

We present an unusual case of cutaneous carcinosarcoma with the epithelial component closely resembling nodular basal cell carcinoma, and the mesenchymal component composed of cells constituting extended follicular papillae. A solitary tumor was excised in an 80-year-old man.

Histologic sections revealed an ulcerated, asymmetric, poorly circumscribed neoplasm composed of epithelial cells arranged in lobules with peripheral palisading or in a cribriform pattern. The epithelial cells were darkly basophilic with scant cytoplasm and round or oval nuclei with an indistinct chromatin pattern and nucleoli. Nuclei crowding and mitotic figures were observed. Some lobules contained melanin. There were no shadow cells, sebaceous or apocrine glandular differentiation. Each epithelial nodule was surrounded by multiple rows of cells with pale vesicular nuclei and scant cytoplasm. Smaller epithelial aggregations were encircled by these cells concentrically; in larger ones these cells were aligned across a broad front resembling so-called "continuous papillae". Additionally, numerous small follicular germ-like structures associated with papillae were seen. The cells composing "continuous papillae" showed nuclear pleomorphism, numerous mitotic figures including atypical ones, and nuclear crowding. At foci, the transition from the multilayered arrangement of these cells into their diffuse proliferation in the stroma was seen. There were no transitions between the epithelial and stromal component; both were intermingled as though being mutually dependent, with no areas revealing a high-grade tumor or dedifferentiation.

Immunohistochemically, the epithelial cell component stained with cytokeratins. The cells of the mesenchymal component tested positive for vimentin and negative for desmin and cytokeratins. The proliferation index (Ki-67) was high in both components. There were also a high number of p53-positive cells in both compartments.

We propose the term "low-grade trichoblastic carcinosarcoma" for this neoplasm. We are not aware of a similar tumor published in the English literature.

Trichoblastic carcinoma ("malignant trichoblastoma") with lymphatic and hematogenous metastases.

Regauer S, Beham-Schmid C, Okcu M, Hartner E, Mannweiler S.

Institute of Pathology, University of Graz Medical School, Austria.

Mod Pathol 2000 Jun;13(6):673-8 Abstract quote

We report an aggressively behaving malignant trichogenic tumor arising in a trichoblastoma (TB) with widespread lymphatic and hematogenous metastases in a 55-year-old man with a concomitant B-cell chronic lymphocytic leukemia.

The primary tumor had been present and unchanged for as long as 40 years before excision. Typical trichogenic TB with dystrophic calcification and even ossification was still present peripheral to the malignant transformation. The malignant neoplasm consisted of basaloid cells, spindle cells arranged in fascicles and densely packed rounded nests or "cell balls." The metastases consisted of immature basaloid cells and cell balls, and the recurrences became successively more undifferentiated. The residual TB reacted with antibodies to cytokeratin (CK) 6, 8, 14, and 17 and focally to S-100; the malignant primary tumor reacted uniformly with antibodies to vimentin and only focally with antibodies to CK and S-100. The metastatic tumor had lost epidermal CK expression but maintained expression of S-100 in paraffin-embedded tissues. Trichoblastic differentiation was confirmed in frozen tissues with antibodies to hair keratins. No expression of p53 or bcl-2 was identified, but p-glycoprotein (MDR-1 gene related) was expressed by primary and metastatic tumor cells.

We believe that this neoplasm is best classified as a trichoblastic carcinoma arising in a TB in association with a B-cell chronic lymphocytic leukemia. This case illustrates that TBs have the potential for malignant transformation and aggressive behavior.


Trichoblastoma with
apocrine and sebaceous differentiation.

Yu DK, Joo YH, Cho KH.

Department of Dermatology, Seoul National University College of Medicine, Seoul, Korea.
Am J Dermatopathol. 2005 Feb;27(1):6-8. Abstract quote  

Trichoblastoma is a rare, benign tumor that differentiates toward the hair germ, the embryonic precursor of a hair follicle. Several cases of trichoblastoma showed multiple differentiation toward more than one type of adnexal structure.

We report a case of a trichoblastoma, which had developed on the scalp as a solitary 1-cm nodule 3 years ago. A histologic examination indicated that the specimen had features of multiple differentiation. In particular, there were occasional foci of decapitation secretion, as well as cells with web-like and bubbly cytoplasm suggesting seboblasts, and a sebaceous duct-like structure. In addition, there were occasional germinative cells in the palisade, and scattered hair papilla-like structures showing follicular differentiation.

An immunohistochemical study showed that the neoplasm, or areas in it, stained positive for low molecular cytokeratin, high molecular cytokeratin, EMA, S-100, and GCDFP-15. This is an unusual case of a trichoblastoma with apocrine and sebaceous differentiation.

Trichoblastic neoplasm with apocrine differentiation.

Usmani AS, Rofagha R, Hessel AB.

Ohio State University (A.S.U., R.R., A.B.H.), University Medical Center, Columbus, Ohio.

Am J Dermatopathol 2002 Aug;24(4):358-60 Abstract quote

Trichoblastoma is a benign neoplasm with primitive hair follicle differentiation. The tumor is characterized by nests and cords of epithelial cells in an organized relation to stroma. The epithelial cells differentiate toward follicular germ and follicular sheath. More divergent differentiation in the form of sebaceous elements in trichoblastoma has infrequently been reported in the literature.

We report a trichoblastic neoplasm showing typical features of trichoblastoma as well as areas of apocrine differentiation. The neoplasm, which was present for several months, was removed from the chin of a 31-year-old woman. Histologic examination showed a neoplasm composed of basaloid nests with occasional papillary mesenchymal bodies as well as ducts and glands exhibiting apocrine differentiation. Trichoblastoma with apocrine features is rarely reported in the literature.


Clear Cell Trichoblastoma in Association With A Nevus Sebaceus

Michael Tronnier, etal.

Am J Dermatopathol 2001;23:143-145 Abstract quote

Nevus sebaceus is a hamartoma that is frequently associated with various neoplasms. Among the neoplasms observed in sebaceus nevi, trichoblastomas are the most common. The present case, to my knowledge, is the first description of a clear cell variant of trichoblastoma.


Some consider this a variant of trichoblastoma

Cutaneous lymphadenoma. A peculiar variant of nodular trichoblastoma.

Diaz-Cascajo C, Borghi S, Rey-Lopez A,
Carretero-Hernandez G.

Department of Pathology, Hospital Notra Sra del Pino, University of Las Palmas, Spain.

Am J Dermatopathol 1996 Apr;18(2):186-91 Abstract quote

Cutaneous lymphadenoma is an uncommon benign epithelial neoplasm with a prominent lymphocytic infiltrate. Both a pilosebaceous and an eccrine origin have been suggested. We herein document three cases of cutaneous lymphadenoma.

Our findings support the hypothesis that cutaneous lymphadenoma is a benign tumor with follicular differentiation representing a peculiar form of nodular trichoblastoma with adamantinoid features and a significant inflammatory cell infiltrate.


Nodular trichoblastoma with adamantinoid features.

Betti R, Alessi E.

Fourth Clinic of Dermatology, Ospedale San Paolo,
Milano, Italy.

Am J Dermatopathol 1996 Apr;18(2):192-5 Abstract quote

We report a cutaneous tumor characterized by follicular differentiation and adamantinoid features that we consider to be part of the histopathologic spectrum of trichoblastoma.

Previously, similar lesions have been reported in the medical literature as cutaneous lymphadenoma or lymphoepithelial tumor of the skin.

Clear Cell Trichoblastoma: A Clinicopathological and Ultrastructural Study of Two Cases.

Kazakov DV, Mentzel T, Erlandson RA, Mukensnabl P, Michal M.

*Sikl's Department of Pathology, Charles University Medical Faculty Hospital, Pilsen, Czech Republic dagger
Dermatohistopathologische Gemeinschaftspraxis, Friedrichshafen,
Germany double daggerDiagnostic Electron Microscopist, South Burlington Vermont.

Am J Dermatopathol. 2006 Jun;28(3):197-201. Abstract quote  

Clear cell change in basal cell carcinomas is a well-recognized phenomenon, but is obviously rare in trichoblastomas.

We present two cases of clear cell trichoblastoma in which clear cell change was very much prominent, and the results of an ultrastructural study intended to explore the basis of that feature.

Both our patients were women, aged 56 and 77 years, who presented with solitary, slowly growing nodules that measured 3 to 5 cm in largest dimension and were located on the scalp and the flexor aspect of the lower arm. Microscopically, the tumors in both cases were symmetric, non-ulcerated, and composed of variably sized and shaped (cribriform, racemiform, strands, cords, nodules) aggregations of monomorphous basaloid epithelial cells that were associated with a specific trichogenic stroma. Common to both tumors was clear cell cytoplasm evident in the majority of the epithelial cells in one case and almost in the entire epithelial cell population in the other. In most epithelial aggregations the epithelial cells with clear cytoplasm often appeared columnar and were arranged in a palisade along a recognizable basal membrane, thus indicative of outer sheath differentiation at the bulb. There were other signs of follicular differentiation.

Ultrastructurally, variably sized clusters of uniform small basaloid epithelial cells were separated from the stroma by a thin discontinuous basement membrane. In addition to the usual organelles, the cytoplasm contained fairly conspicuous tonofilaments and variably sized vacuoles devoid of a limiting membrane, located between the palisaded nuclei and the outer cell membrane.

The majority of vacuoles were empty, although clumps of a finely granular substance were occasionally evident. No distinct lipid droplets or glycogen particles were identified. The basaloid cells were joined by scattered small desmosomes. These findings were consistent with trichilemmal differentiation at the bulb.

Melanotrichoblastoma: immunohistochemical study of a variant of pigmented trichoblastoma.

Kanitakis J, Brutzkus A, Butnaru AC, Claudy A.

Am J Dermatopathol 2002 Dec;24(6):498-501 Abstract quote

Trichoblastomas (TBs) are benign skin tumors recapitulating the differentiation of hair follicles. Several pathologic variants have been described, including the rare pigmented TB.

We report a deeply pigmented nodular tumor excised on the scalp of a 32-year-old African woman, which was clinically suggestive of blue nevus or melanoma. Histologically, the tumor presented features of TB, remarkable by virtue of heavy melanin deposits found within and around tumor nests. By immunohistochemistry, abundant dendritic melanocytes with features of hair follicle melanocytes (expression of S100 protein, tyrosinase, and, most importantly, gp100/HMB-45) were found within the tumor masses.

By analogy with melanoacanthoma, a tumor consisting of a combined proliferation of epidermal keratinocytes and melanocytes, we called this tumor "melanotrichoblastoma" and view it as a peculiar variant of (pigmented) TB.


Pigmented trichoblastoma.

Aloi F, Tomasini C, Pippione M.

Department of Dermatology, University of Turin, Italy.

Am J Dermatopathol 1992 Aug;14(4):345-9 Abstract quote

We report a case of trichogenic tumor with epithelial and mesenchymal components recapitulating the formation of hair germs.

The epithelial lobules were highly pigmented and affected the full thickness of the dermis, extending into the subcutaneous fat. In addition, amyloid deposits were found within the epithelial lobules and in the stroma. The overall architecture was reminiscent of hair bulbs. Problems of differential diagnosis with other trichogenic tumors and pigmented tumors are discussed.

Trichoblastoma arising within an apocrine poroma.

Santos-Briz A, Rodriguez-Peralto JL, Miguelez A, Lopez-Rios F.

Departamento de Anatomia Patologica, Hospital Universitario "12 de Octubre," Madrid, Spain.


Am J Dermatopathol 2002 Feb;24(1):59-62 Abstract quote

A poroma is a benign neoplasm composed of poroid and cuticular cells and is thought to derive from the eccrine duct.

Several recent reports have described cases with sebaceous, follicular, and apocrine differentiation, suggesting a possible apocrine origin, however. Trichoblastoma is a rare benign tumor composed of germinative cells related to the folliculosebaceous-apocrine unit.

We report a unique case of a trichoblastoma arising within a poroma with apocrine and sebaceous differentiation. To our knowledge, this exceptional association has not been described previously and may support the theory of the apocrine origin of poromas.


Rippled-pattern sebaceous trichoblastoma.

Graham BS, Barr RJ.

Department of Dermatology, University of California, Irvine, USA.

J Cutan Pathol 2000 Oct;27(9):455-9 Abstract quote

BACKGROUND: There is a large spectrum trichoblastoma; of which, several histologic variants have been described including a rippled-pattern variant. Three cases of rippled-pattern trichoblastoma are described which also exhibited definitive foci of sebaceous differentiation.

METHODS: Three cases were retrieved from the archives of the Dermatopathology Laboratory at the University of California Irvine (Orange, CA, USA). All specimens were stained with hematoxylin and eosin (H&E). In addition, sections were submitted for immunohistochemical studies with epithelial membrane antigen (EMA).

RESULTS: All three biopsies were composed of well-circumscribed multiple variously sized tumor lobules present in the upper to deep dermis comprised of with rounded or slightly elongated basaloid cells with scant eosinophilic cytoplasm. The lobules were separated by a slightly hyalinized stroma. The unique finding present in all three specimens was a peculiar arrangement of the basaloid cells in linear rows parallel to one another. This gave the tumors a rippled pattern similar to the palisading of nuclei of Verocay bodies seen in schwannomas. In addition all three biopsies showed definite sebaceous differentiation.

CONCLUSIONS: Three additional cases of rippled-pattern trichoblastoma are presented. All three were located on the scalp and showed additional features of foci of sebaceous differentiation. No associations with Muir-Torre Syndrome were found in these patients. Because this appears to be a distinct variant within the large spectrum of trichoblastoma, the term rippled-pattern sebaceous trichoblastoma is suggested.

A rippled-pattern trichoblastoma: an immunohistochemical study.

Yamamoto O, Hisaoka M, Yasuda H, Nishio D, Asahi M.

Department of Dermatology and Occupational Dermatopathology, School of Medicine, University of Occupational and Environmental Health Japan, Kitakyushu.

J Cutan Pathol 2000 Oct;27(9):460-5 Abstract quote

BACKGROUND: Since the first description by Hashimoto et al., there have been only a few case reports of rippled-pattern tricogenic tumor. In addition, there are no reports on detailed immunohistochemical analyses of this rare neoplasm. We describe here an additional case of rippled-pattern trichogenic tumor with a special reference to its immunohistochemical features.

METHODS: A nodule arising on the occipital area of a 62-year-old Japanese woman was histologically and immunohistochemically investigated.

RESULTS: Histopathologically, the lesion contained various-sized lobular nests, which consisted of oval to elliptical shaped basaloid cells without any atypia and were embedded in the collagenous stroma. Some elongated basaloid cells were arranged in a palisading fashion forming parallel rows of epithelial ribbons in a rippled-pattern. Cytokeratin (CK) immunohistochemistry showed constant expressions of CK1/5/ 10/14, CK5/8, CK14 and CK7, and focal expressions of CK17 and CK19 in the basaloid cells, suggesting a keratin phenotypical similarity to the cells in small nodular type trichoblastoma.

CONCLUSIONS: The present tumor is a variant of trichoblastoma, and considered to be in close association with the outer root sheath and/ or follicular germinative cells.


Subcutaneous trichoblastoma.

Kaddu S, Schaeppi H, Kerl H, Soyer HP.

Department of Dermatology, University of Graz, Austria.

J Cutan Pathol 1999 Nov;26(10):490-6 Abstract quote

We have recently observed three examples of solitary trichoblastomas (TB) with unusual histopathologic features characterized mainly by numerous aggregations of basaloid cells limited to the subcutis.

The three trichoblastomas with unusual features were identified from a large series of 38 solitary TB cases collected over a period of 20 years. Clinically, all three neoplasms presented in men (49, 52, and 62 years old) as solitary, 1- to 1.5-cm skin-colored nodules situated on the scalp, face, and lower arm, respectively. Histopathologically, they showed numerous, smooth-bordered aggregations of basaloid cells limited to the subcutis and surrounded by a sclerotic and partly hyalinized stroma. Multiple sections revealed no connections of basaloid aggregations to the overlying epidermis or pre-existing follicular structures. All three cases displayed rather unusual morphologic growth patterns, including areas of variously sized, nodular aggregations of basaloid cells and extensive foci of elongated, thin columns and branching cords of basaloid cells. A striking feature in the stromal component in two cases was the presence of large, prominent areas of hyalinization and sclerosis. Characteristically, all three neoplasms showed numerous foci with rudimentary follicular germs and papillae. Cytomorphologically, the basaloid cells exhibited dark staining nuclei with large prominent nucleoli and scanty, pale or eosinophilic cytoplasm. Variable number of mitotic figures (2-4 mitoses per high-power field) and single necrotic cells were noted. In one case, small, foci of necrosis en masse were observed. Follow-up data after total excision in all three cases (80, 69, and 6 months) revealed no local recurrences.

In light of our observations, we suggest that subcutaneous TB represents a rare variant of solitary TB. Besides the exclusive subcutaneous location, this neoplasm also displays a constellation of particular histopathologic features, namely, rather complex epithelial growth patterns and stroma with prominent foci of sclerosis and hyalinization.

Trichoblastic Sarcoma: A High-grade Stromal Tumor Arising in Trichoblastoma.

From the *Departments of Pathology, University of Pavia and I.R.C.C.S. S. Matteo Hospital, Pavia, Italy; daggerDermatology, University of Pavia and I.R.C.C.S. S. Matteo Hospital, Pavia, Italy; and double daggerDivision of Oncologic Surgery, S. Marco Hospital, Zingonia, Italy.


Am J Dermatopathol. 2007 Feb;29(1):79-83. Abstract quote

We report a case of primary sarcoma of the skin with a biphasic histological pattern, being composed of areas of mixed mesenchymal-epithelial cell proliferation and areas of purely sarcomatous growth.

The tumor occurred in the posterior cervical region of a 93-year-old man, and its history was marked by sudden, rapid enlargement after many years of stable duration. The excised lesion was about 4 cm in diameter, had a firm consistency and was covered by intact skin.

Histological examination showed a multifocal proliferation of follicular germinative cells arranged in corymbiform and petaloid shapes with an overall retiform growth pattern. Epithelial cords and strands were composed of cytologically uniform cells with bland nuclear features and were surrounded by a prominent, fibroblast-rich stroma reminiscent of a perifollicular sheath. In many areas of the tumor the stroma showed abrupt transition into a pleomorphic proliferation of large sarcomatous cells with frequent and often atypical mitoses. Multinucleated neoplastic cells infiltrated the epithelial structures to cause their partial or total obliteration in many fields of the lesion. Immunohistochemically, the epithelial cells displayed expression of various keratins, with a particularly intense staining for 34betaE12, and were partly positive for the CD10 antigen. A strong immunostaining for this antigen was also observed in malignant-appearing stromal areas, where no expression of cytokeratins was detected. Moreover, nuclear positivity for p53 protein was seen in sarcomatous cells, whereas it resulted in total lack of epithelial elements.

Our case emphasizes that high-grade sarcoma may occur in the spectrum of trichoblastic tumors and that it may share some features of other noncutaneous biphasic neoplasms, such as mammary cystosarcoma phyllodes.

Androgen receptor expression helps to differentiate basal cell carcinoma from benign trichoblastic tumors.

Izikson L, Bhan A, Zembowicz A.

Department of Dermatology, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA.

Am J Dermatopathol. 2005 Apr;27(2):91-5. Abstract quote  

Histologic differentiation between basal cell carcinoma and benign trichoblastic neoplasms such as trichoepithelioma and trichoblastoma can be difficult on small biopsies. Therefore, several attempts have been made to identify immunohistochemical differences between these entities. Recent studies have shown androgen receptor expression in a number of mature epithelial structures in the skin and in epithelial neoplasms including basal cell carcinoma. In contrast, androgen receptor expression was absent in mature hair follicles or the few trichogenic neoplasms studied to date. These findings suggested that androgen receptor expression might be a useful adjunct in the histologic differential diagnosis between basal cell carcinoma and benign trichoblastic neoplasms.

Therefore, we performed immunohistochemical analysis of androgen receptor expression in 32 basal cell carcinomas and 10 benign trichoblastic tumors (6 trichoepitheliomas and 4 trichoblastomas). In our study, at least focal expression of androgen receptor was detected in 78% of basal cell carcinomas. None of the trichoblastic tumors showed any androgen receptor immunoreactivity.

These results confirm the lack of expression of androgen receptor in benign trichoblastic neoplasms and indicate that androgen receptor expression by tumor cells points to basal cell carcinoma as the most likely diagnosis.
CD10 expression in trichoepithelioma and basal cell carcinoma*.

Pham TT, Selim MA, Burchette JL Jr, Madden J, Turner J, Herman C.

Department of Pathology, Duke University Medical Center, Durham, NC, USA.

J Cutan Pathol. 2006 Feb;33(2):123-8. Abstract quote  

Background: Trichoepithelioma (TE) is a benign neoplasm that shares both clinical and histologic features with basal cell carcinoma (BCC). However, it is important to distinguish these neoplasms. Limited immunohistochemical stains are available to separate these two tumors.
Methods: CD10 protein immunohistochemistry was performed on paraffin-embedded biopsies of 13 TE and 23 BCC diagnosed by routine microscopy. Cases were analyzed for pattern of CD10 expression by tumor cells and surrounding stroma.
Results: Twelve of 13 (92%) TE showed positive stromal immunoreactivity. Of these, eight cases also demonstrated positivity of the papilla, and two also showed positivity of the basaloid cells. No TE demonstrated epithelial expression alone. On the other hand, expression of CD10 by basaloid cells was identified in 20 (87%) cases of BCC. Stromal positivity was also identified in three cases of BCC. Condensation of CD10-positive stromal cells around basaloid nests was statistically significant in differentiating TE from BCC (p < 0.0001). Conversely, CD10-positive basaloid cells were seen predominantly in BCC (p < 0.0001).
Conclusions: This study demonstrates a statistically significant difference in CD10 staining pattern between TE and BCC. Thus, CD10 may be a useful adjunct marker in distinguishing these tumors.

Trichoblastoma and basal cell carcinoma are neoplasms with follicular differentiation sharing the same profile of cytokeratin intermediate filaments.

Schirren CG, Rutten A, Kaudewitz P, Diaz C, McClain S, Burgdorf WH.

Department of Dermatology, Ludwig-Maximilians-University, Friedrichshafen, Germany.

Am J Dermatopathol 1997 Aug;19(4):341-50 Abstract quote

Trichoblastoma and nodular basal cell carcinoma are generally held to be distinctive epithelial neoplasms with some overlapping features.

We investigated 30 trichoblastomas in which the basaloid cells expressed cytokeratins (CK) CK5/6, CK14, CK17, CK19, and, in a few cells, vimentin.

The cells of the periphery of small and large cysts showed the same profile. Cells lining the lumen of small cysts expressed CK14, CK17, and involucrin, and those in larger cysts showed a positivity for CK1, CK4, CK10, CK14, CK17, and involucrin. The remaining tested antibodies (CK7, CK8, CK13, CK18, CK20, alpha-smooth-muscle actin) were negative in all cases. The cells of the stroma expressed vimentin and in 22 cases, the CD34 antigen. Seventeen nodular basal cell carcinomas showed exactly the same staining pattern. Furthermore, there are striking immunohistochemical similarities between the neoplastic basaloid cells of both neoplasms and the cells of the hair germ.

Therefore, trichoblastoma and nodular basal cell carcinoma cannot be distinguished by their pattern of cytokeratin expression in paraffin sections. The virtually identical cytokeratin pattern seen in trichoblastoma, basal cell carcinoma, and the developing fetal hair follicle is compelling evidence for common differentiation pathway.

Cytokeratins as Markers of Follicular Differentiation An Immunohistochemical Study of Trichoblastoma and Basal Cell Carcinoma

Hjalmar Kurzen, M.D.; Lorenz Esposito; Lutz Langbein, Ph.D.; Wolfgang Hartschuh, M.D.

From the Department of Dermatology, University of Heidelberg (H.K., L.E., W.H.), and Division of Cell Biology, German Cancer Research Center (L.L.), Heidelberg, Germany

Am J Dermatopathol 2001;23:501-509 Abstract quote

Trichoblastoma(s) (TB) are benign neoplasms of follicular differentiation frequently found in nevus sebaceus. Many morphologic features are shared with nodular basal cell carcinoma(s) (BCC), sometimes rendering the differential diagnosis difficult.

Because both neoplasms can simulate components of mature hair follicles histologically, we attempted to corroborate this by immunohistochemical examination of cytokeratins and hair keratins differentially expressed in the hair follicle. Trichoblastoma(s) and BCC showed homogenous expression of CK14 and CK17. The innermost cells of the tumor nodules in all TB and in 72% of BCC were positive for CK6hf. Using a specific CK15 antibody, 38% of TB showed a focal labeling and all BCC remained negative; 70% of TB and 22% of BCC expressed CK19. CK8 was expressed by numerous Merkel cells present in all TB but in none of the BCC examined. All type I and II hair keratins tested, (especially hHa1, hHa5, and hHa8) remained negative in all tumors examined.

Trichoblastoma(s) and BCC show consistent expression of CK6hf, CK14, and CK17; variable expression of CK15 and CK19; and absence of hair keratins. This indicates a differentiation toward the outer root sheath epithelium or the companion layer and not toward the inner root sheath, matrix, or cortex.



Cytokeratin expression in trichoblastic fibroma (small nodular type trichoblastoma), trichoepithelioma and basal cell carcinoma.

Yamamoto O, Asahi M.

Department of Dermatology and Occupational Dermatopathology, University of Occupational and Environmental Health, Japan

Br J Dermatol 1999 Jan;140(1):8-16 Abstract quote

Classical trichoblastic fibroma or small nodular type trichoblastoma (Ackerman) is a rare tumour. This tumour, trichoepithelioma and basal cell carcinoma (BCC) have some overlapping histopathological features. There are only a few reports on immunohistochemical studies in large series of these three neoplasms.

We investigated immunostaining patterns of 10 different anticytokeratin (CK) antibodies and several other markers in these neoplasms, comparing them with the patterns in normal adult and fetal skin. In trichoblastic fibroma (three cases), CK1/5/10/14, CK7, CK8/18, CK10/11, CK14, CK17 and CK19 were expressed in the basaloid nests, and CK6 and involucrin were detected in the inner layers of keratinous cysts. Trichoepithelioma (seven cases) expressed CK1/5/10/14, CK8/18, CK14, CK17 and CK19 in the basaloid nests, and CK6, CK10, CK10/11 and involucrin were positive in the keratinous cysts. However, no CK7 expression was observed. Solid and keratotic types of BCC (29 cases) expressed CK1/5/10/14, CK7, CK8/18, CK14, CK17 and CK19 in the basaloid nests. The keratinous cysts in BCC were stained with anti-CK6, CK10, CK10/11 and involucrin antibodies. Coupled with the expression of CK8/18, CK17 and CK19 in the outer root sheath of the adult hair follicle, these three neoplasms shared a keratin phenotype characteristic of the outer root sheath.

Judging from our immunohistochemical results, trichoblastic fibroma and BCC cannot be differentiated by their patterns of CK expression. The expression of CK7, which is noted in fetal hair follicles, trichoblastic fibroma and BCC, suggests the presence of subpopulations that retain fetal phenotypic characteristics in these two neoplasms.

Although the current concept regards trichoepithelioma and trichoblastic fibroma as a single tumour group, the lack of CK7 expression in trichoepithelioma supports the notion that the two are different.

Immunohistochemical comparison of cutaneous lymphadenoma, trichoblastoma, and basal cell carcinoma: support for classification of lymphadenoma as a variant of trichoblastoma.

McNiff JM, Eisen RN, Glusac EJ.

Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut, USA

J Cutan Pathol 1999 Mar;26(3):119-24 Abstract quote

Cutaneous lymphadenoma is an uncommon basaloid epithelial tumor of uncertain histogenesis, most recently classified as a variant of trichoblastoma. Because characteristic immunohistochemical findings have been reported in trichoblastomas, we evaluated the staining patterns of five cutaneous lymphadenomas and compared the results to those of ten trichoblastomas and ten nodular basal cell carcinomas (BCCs), using antibodies to cytokeratin 20 (CK20), bcl-2, and CD34. In addition, because lymphadenomas contain intraepithelial S100-positive putative Langerhans cells, we compared staining of all tumor groups for S100 protein and CD1a. We also attempted to corroborate recent reports of CD30-positive activated lymphocytes in lymphadenomas.

We identified CK20-positive Merkel cells in 3/5 lymphadenomas, 7/10 trichoblastomas, and none of the BCCs. Staining for bcl-2 accentuated the peripheral epithelial layer in all lymphadenomas and in 3/10 trichoblastomas, while the remaining trichoblastomas and all BCCs stained diffusely. There was stromal staining with CD34 in two lymphadenoma, 4 trichoblastomas, and 3 BCCs. All lymphadenomas featured numerous intraepithelial S100-positive cells which were also positive for CD1a in three cases tested. In addition, 8/10 trichoblastomas and 2/10 BCCs contained modest numbers of cells labelling for S100 and CD1a. Two of three lymphadenomas contained rare single cells resembling histiocytes faintly positive for CD30, and similar cells labelled for CD68.

We conclude that the similar staining patterns of lymphadenomas and trichoblastomas support the classification of lymphadenoma as a variant of trichoblastoma. Staining with CD34 does not reliably distinguish between these tumors and BCCs. Lymphadenomas, trichoblastomas, and BCCs may all contain Langerhans' cells. The relationship between these cells and the striking lymphoid infiltrates seen in lymphadenomas is not clear. In our cases, the CD30-positive cells in lymphadenomas appear to represent histiocytes rather than activated lymphocytes.

Macpherson and Pincus. Clinical Diagnosis and Management by Laboratory Methods. Twentyfirst Edition. WB Saunders. 2006.
Rosai J. Ackerman's Surgical Pathology. Ninth Edition. Mosby 2004.
Sternberg S. Diagnostic Surgical Pathology. Fourth Edition. Lipincott Williams and Wilkins 2004.
Robbins Pathologic Basis of Disease. Seventh Edition. WB Saunders 2005.
DeMay RM. The Art and Science of Cytopathology. Volume 1 and 2. ASCP Press. 1996.
Weedon D. Weedon's Skin Pathology Second Edition. Churchill Livingstone. 2002
Fitzpatrick's Dermatology in General Medicine. 6th Edition. McGraw-Hill. 2003.
Weiss SW and Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors. Fourth Edition. Mosby 2001

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