Familial nonmedullary thyroid neoplasia.

Thyroid carcinoma accounts for less than 1% of all human malignancies and carries one of the highest overall familial relative risks as compared with cancers from other sites. This is particularly true for medullary carcinoma, as well as for carcinomas of follicular cell origin in general, where inheritance has been implicated in 2.5 to 6.3% of the cases. Familial nonmedullary thyroid tumors show a variety of genetic mechanisms implicated in thyroid tumorigenesis and occur in several tumor-prone traits (e.g., familial adenomatous polyposis [FAP] and Cowden's disease [CD]) or as the only or dominant inherited manifestation. The latter group includes the most common familial papillary carcinoma, in which environmental factors such as radiation exposure may also play an important etiological role. Familial follicular cell tumors show a variety of morphological features ranging from benign thyroid nodulation to carcinoma, usually develop in young individuals, and tend to be multicentric--an indication for total thyroidectomy to avoid tumor recurrence and potential risk of malignant transformation. The pathologist may play an important role in the histological interpretation of familial nonmedullary thyroid tumors, which may lead to further clinicogenetical investigations of the affected patient and family screening. Familial follicular cell thyroid neoplasms show a complex molecular biological pathway of tumorigenesis when compared between themselves and with their sporadic counterparts.