Biological Behavior of Papillary Carcinoma of the Thyroid Including Squamous Cell Carcinoma Components and Prognosis of Patients Who Underwent Locally Curative Surgery

Thyroid carcinoma showing squamous differentiation throughout the entire lesion is diagnosed as squamous cell carcinoma of the thyroid (SCCT) in the WHO classification. This entity is a rare disease and shows a dire prognosis; however, squamous differentiation is more frequently detected in only a portion of papillary thyroid carcinoma. In this paper, we present our experience of 10 patients (8 primary lesions and 2 with recurrence in the lymph nodes) with papillary thyroid carcinoma having an SCC component (PTC-SCC). Only 3 of 8 primary lesions (38%) and none of the 2 recurrent nodes were preoperatively diagnosed as or suspected of having SCC components. All 10 patients underwent locally curative surgery. To date, 3 patients have died of carcinoma, and 2 had distant metastasis at diagnosis or had an undifferentiated carcinoma component. The other 7 are currently alive 5 to 43 months after diagnosis. Systemic adjuvant therapy after the detection of recurrence was effective for 2 patients. It is possible that some PTC-SCC patients without distant metastasis who undergo locally curative surgery can survive for a prolonged period and adjuvant therapies can be effective for local and distant recurrences.