Background: Papillary carcinoma is the most common type of thyroid cancer. Cases of papillary carcinoma merging with squamous carcinoma, mucoepidermoid carcinoma, insular carcinoma, columnar cell carcinoma, poorly differentiated carcinoma, anaplastic carcinoma and medullary carcinoma have been reported to date.
Case: A 62-year-old female presented with a 3-cm, hard and painful tumor in the right lobe of the thyroid gland. Fine needle aspiration biopsy yielded a diagnosis of undifferentiated (anaplastic) carcinoma. The tumor was deemed a papillary and mucoepidermoid carcinoma of the thyroid with anaplastic transformation on histology. On retrospective review, the aspirates showed cytologic features of papillary, mucoepidermoid and anaplastic carcinoma. Cellular sheets showing a combination of squamous and mucin-producing features and microcystic like pattern containing hyaline bodies and/or amorphous material correlated well with the histologic and ultrastructural features of mucoepidermoid carcinoma. To our knowledge, no other case with these cytologic characteristics has been reported previously.
Conclusion: This case illustrates that fine needle aspiration biopsy can be used to recognize rare malignant thyroid neoplasms showing a combination of papillary, mucoepidermoid and undifferentiated carcinoma.