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Background

The follicular adenoma of the thyroid is a common benign tumor of the thyroid gland. They present as a solitary nodule, usually as a painless mass. It may be found during a routine physical examination. A physician may order a nuclear medicine thyroid scan which measures uptake of radionucleotide labelled iodine. Adenomas are usually cold nodules since they usually take up less radioactive iodine than normal surrounding gland. On the other hand, about 10% of cold nodules are malignant. Conversely, hot nodules are only rarely malignant.

Once the nodule is identified, additional diagnostic techniques including an ultrasound examination which may identify a cystic component may be helpful. A pathologist may perform a fine needle aspiration biopsy to obtain diagnostic cytology. In the case of a follicular adenoma, a diagnosis of follicular neoplasm-adenoma versus carcinoma, may be rendered. On cytologic examination, a pathologist cannot make the distinction between an adenoma versus a carcinoma. An excisional biopsy must be obtained. The pathologist must carefully embed the entire capsule in order to exclude capsular invasion, the hallmark of malignancy.

EPIDEMIOLOGIC ASSOCIATIONS CHARACTERIZATION
EXTERNAL RADIATION Variable delay after exposure
May show aggressive features

Risk of thyroid carcinoma in a female population after radiotherapy for breast carcinoma.

Huang J, Walker R, Groome PG, Shelley W, Mackillop WJ.

The Radiation Oncology Research Unit, Department of Oncology, Queen's University, Kingston Regional Cancer Center, Kingston, Ontario, Canada.

Cancer 2001 Sep 15;92(6):1411-1418 Abstract quote

BACKGROUND: There is increasing concern regarding the risk of developing a second primary tumor in adjacent organs as a result of scattered radiation among patients who have undergone radiotherapy (RT) for breast carcinoma. Previous studies have focused mainly on the possible increase in the incidence of contralateral breast carcinoma. To the authors' knowledge, the risk of thyroid carcinoma among these women has not been explored to date.

METHODS: In this population-based, retrospective cohort study, the authors identified 194,798 women who were diagnosed with invasive breast carcinoma (exclusive of those with distant metastasis) between 1973 and 1993, and ascertained subsequent cases of thyroid carcinoma utilizing data from the Surveillance, Epidemiology, and End Results (SEER) program of the U.S. National Cancer Institute. Poisson regression was used to calculate the age-standardized incidence ratio (SIR) of thyroid carcinoma and to model the influence of RT on the relative risk (RR) between the RT cohort (48,495 women) and the non-RT cohort (146,303 women).

RESULTS: A total of 28 women in the RT cohort and 112 women in the non-RT cohort subsequently developed thyroid carcinoma. The distribution of thyroid carcinoma histologies in both the RT cohort and the non-RT cohort was similar to that in the female general population. Overall, there was no significant increase in the risk of thyroid carcinoma in either the RT cohort or the non-RT cohort compared with the general population; the SIR was 1.1 (95% confidence interval [95% CI], 0.8-1.6) for the RT cohort and 1.2 (95% CI, 1.0-1.4) for the non-RT cohort. When the RT cohort was compared with the non-RT cohort, the RR of thyroid carcinoma was 1.0 (95%CI, 0.7-1.5).

CONCLUSIONS: The risk of radiation-associated thyroid carcinoma after initial RT for breast carcinoma was so low as to be undetectable in the current large population-based study. Continued monitoring of these women will be required to document that these findings are maintained with even longer follow-up periods. However, with 10,895 women having been followed for > 10 years at the time of last follow-up in the current study, these findings should be reassuring to women considering RT for their breast carcinoma. Therefore, women who have received RT for breast carcinoma require no special surveillance for their thyroid gland. Furthermore, previous breast radiation need not be a factor in determining the optimal management of thyroid nodules arising in women who received RT for breast carcinoma.

 

PATHOGENESIS CHARACTERIZATION
TSH receptor

Couples the alpha subunit of the stimulating guanine nucleotide binding protein Gs

This activates adenylate cyclase leading to intracellular increases of cAMP

This activates genes that control the production of thyroid hormone and proliferation of thyroid epithelial cells

Somatic mutations

Mutations occurring in the components of the signalling system may cause chronic stimulation of the cAMP pathway

Somatic mutations found in Gsalpha in 12-38% of adenomas

 

GROSS APPEARANCE/CLINICAL VARIANTS CHARACTERIZATION
General

Solitary, spherical and encapsulated tumor demarcated from the surrounding thyroid gland

Average 3 cm in diameter

May range up to 10 cm

 

HISTOLOGICAL TYPES CHARACTERIZATION
GENERAL Uniform appearing follicles containing colloid
Colloid Large colloid filled follicles
Fetal Numerous small well developed follicles lined by flattened epithelial cells
Trabecular Closely packed cells forming cords or trabeculae
Hurthle Large eosinophilic granular cells
Atypical adenomas Pleomorphism and variability in cell and nuclear size

Papillary adenomas

Papillary excrescences within large follicular or cystic spaces
SPINDLE CELL METAPLASIA  

Spindle Cell Metaplasia of the Thyroid Arising in Association With Papillary Carcinoma and Follicular Adenoma

JoAnne Vergilio, MD, Zubair W. Baloch, MD, PhD, and Virginia A. LiVolsi, MD

Am J Clin Pathol 2002;117:199-204 Abstract quote

Spindle cell proliferations of the thyroid have been described in association with reactive processes and aggressive malignant neoplasms.

We describe spindle cell proliferations in 10 patients arising in association with papillary carcinoma and follicular adenoma. The spindle proliferations were 0.3 to 3.0 cm in size, constituted from 1% to 95% of the primary neoplasm, and were either admixed with the neoplastic elements or peripherally located within the primary tumor.

Cytologically, these proliferations showed bland-appearing spindle cells with fine chromatin and subtle nucleoli. Mitoses were rare, and inflammation was minimal. Immunostains showed reactivity with thyroglobulin, indicating their follicular origin. We believe it is important to recognize these metaplastic proliferations and distinguish them from aggressive malignant neoplasms.

 

PROGNOSIS AND TREATMENT CHARACTERIZATION
Treatment Simple excision

Diagnostic Surgical Pathology Third Edition. Sternberg S. Editor. Lippincott Williams Wilkins 1999.


Commonly Used Terms

Follicular Carcinoma of the Thyroid

Thyroid


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Last Updated 2/14/2002

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