Medullary thyroid carcinoma with melanin production--a case report.

Melanin production in medullary thyroid carcinomas is rare. The present case illustrates melanin and other atypical features of medullary carcinoma of the thyroid in a fifty year old female. The diagnosis was suggested on the cytomorphological features seen on fine needle aspiration cytology smears. On histo-pathological examination the tumor was extensively pigmented with frequent mitosis. Amyloid was conspicuously scarce. Confirmation of diagnosis was done by immunohistochemical positivity for calcitonin and HMB-45 on tissue sections. The case is being presented in view of its rarity and distinct immunoreactivity. Review of literature is done and the implications of such dual positivity in the histogenesis and divergent phenotype of this tumor are discussed.