Cribriform-morular variant of papillary carcinoma: a distinctive variant representing the sporadic counterpart of familial adenomatous polyposis-associated thyroid carcinoma?

Abstract

We describe herein four cases of an unusual sporadic thyroid tumor that shares the morphologic features of a distinctive follicular cell neoplasm previously proposed as a feasible indicator of familial adenomatous polyposis. We also review five other similar cases reported in the literature. All of the nine patients were young women, aged 16 to 30 years. Grossly, the neoplasms measured 1.5 to 5.6 cm; they were solid and solitary, except one case, which showed two tumor nodules, one in each lobe. Histologically, the lesions were encapsulated, and they exhibited an intricate blending of cribriform, follicular, papillary, trabecular, and solid patterns of growth, with morular (squamoid) areas. Cribriform structures were prominent, being formed by anastomosing bars and arches of cells in the absence of intervening fibrovascular stroma. Follicular areas were usually devoid of colloid, and the papillae were lined by columnar cells. There were focal areas of trabecular arrangement reminiscent of hyalinizing trabecular adenoma. The tumor cells were cuboidal or tall, with frequent nuclear pseudostratification and abundant eosinophilic-to-oxyphilic cytoplasm. The nuclei were usually hyperchromatic, but nuclear grooves, pale or clear nuclei, and intranuclear cytoplasmic inclusions were variably present. Morules with peculiar nuclear clearing caused by biotin accumulation were scattered in the tumors. Vascular and/or capsular invasion were noted in all of the cases except one, and lymph node metastasis was found in two cases. Immunohistochemical stains showed reactivity for thyroglobulin, epithelial membrane antigen, cytokeratins (including 34betaE12), vimentin, estrogen and progesterone receptors, bcl-2, and Rb proteins. Follow-up in seven cases showed that all of the patients were alive with no evidence of disease at 1 to 13 years after diagnosis. Thus, the behavior of this variant seems to be similar to that of conventional papillary carcinoma Because of the distinctive histologic features, we propose naming this tumor the cribriform-morular variant of papillary carcinoma.