FAMILIAL ADENOMATOUS POLYPOSIS ASSOCIATED THYROID-CARCINOMA - A DISTINCT TYPE OF FOLLICULAR CELL NEOPLASM

Thyroid carcinoma has been described as occurring more frequently than expected in association with familial adenomatous polyposis. The hist ology of these cases has not been described in detail, although the re ported cases were usually diagnosed as papillary carcinoma. We now rep ort the pathological features of four cases of thyroid carcinoma assoc iated with familial adenomatous polyposis, and review the findings in the literature. The tumours in these four cases were all of follicular cell origin as shown by thyroglobulin immunohistochemistry. In three they were multifocal. The tumours showed some features of papillary ca rcinoma-grooved nuclei and papillary architecture, but these were not consistent. They also showed features that were unusual for papillary carcinoma-a cribriform pattern and solid areas with spindle cell compo nent. Commonly the tumours combined both patterns. A review of the rep orted cases of thyroid cancer associated with familial adenomatous pol yposis showed that they also were commonly multifocal and occurred pre dominantly in young women. When the histology was adequately reported or illustrated it was, in most instances, consistent with the findings in our own cases. We therefore suggest that these thyroid tumours for m a distinct type with some unusual features. Clearly it is likely tha t the APC gene is associated with their pathogenesis, and that other f actors contribute to the predominantly female incidence in this as in sporadic tumours. Six of 63 reported cases showed metastasis or died f rom thyroid carcinoma. In a number of cases the tumours presented befo re the familial adenomatous polyposis was recognized. The findings of these unusual histological features in a thyroid tumour, and particula rly of multicentricity, should alert the pathologist to the possibilit y of familial adenomatous polyposis with its implications for family s creening. The tumours are often well demarcated but, because of the mu lticentricity, total thyroidectomy should be advocated.