Clear Cell Variant of Thyroid Carcinoma: A Clinicopathologic Study
Nicole A Cipriani, William C Faquin, Peter M Sadow. Massachusetts General Hospital, Boston, MA
Background: Clear cell carcinoma of the thyroid is classified by the WHO as a variant of follicular or papillary thyroid carcinoma. Clear cell change in thyroid carcinoma has been reported in the literature, often in relation to the differential diagnosis of metastatic clear cell renal cell carcinoma. In modern practice, immunohistochemistry renders this distinction relatively facile. In this study, we address the clinicopathologic characteristics of primary thyroid neoplasms with cytoplasmic clear features.
Design: Our pathology department database was queried for the words "thyroid carcinoma" and "clear cell," resulting in 21 primary thyroid carcinomas from 20 patients from 1992-2012. These 21 cases represent 0.5% of the total in-house thyroid carcinomas (4330) during this time frame.
Results: Of the 21 carcinomas, 12 (57%) were follicular carcinoma (FTC), 5 were conventional papillary carcinoma (PTC), 3 were follicular variant of PTC, and 1 was poorly differentiated carcinoma (PDC). Clear cell change in all cases was focal or multifocal, never diffuse. The average tumor size was 2.8 cm among 12 female and 8 male patients with an average age of 55 years (range: 26 – 80). Five (24%) carcinomas were metastatic to regional lymph nodes (3 FTC and 2 PTC), and two (10%) were metastatic to bone, both FTC. Disease confined to the thyroid (67%) and rates of regional lymph node metastasis (24%) were both near the national averages (68% and 25%, respectively). Distant metastasis (10% in this study) was slightly higher than the 5% national average. The patient with PDC died 1 year after diagnosis, and a patient with metastatic FTC died 2 years after diagnosis. No other deaths were reported. Overall mortality was 10%, which matched national averages when adjusted for age (17% of patients aged 55-64 and 25% of patients aged 65-74).
Conclusions: Clear cell change in thyroid carcinoma is rare and found focally or multifocally within a given lesion. Our findings indicate that clear cell change is more common in FTCs, and is associated with an increased risk of distant metastasis but with a prognosis that is similar to other differentiated thyroid carcinomas.
Wednesday, March 6, 2013 1:00 PM
Poster Session VI # 55, Wednesday Afternoon