Lymphocytic infiltration in pediatric thyroid carcinomas.

Lymphocytic thyroiditis has been associated with an increase in the incidence of thyroid papillary carcinoma in some reports, mostly series of both adults and children. Relatively little is written about thyroiditis and follicular carcinomas. We have seen several cases of pediatric follicular thyroid carcinomas, that had an associated lymphocytic infiltrate, which led us to examine all primary malignant thyroid neoplasms in our surgical files from 1984 through 2000 to examine this relationship. We also investigated the nature of the lymphocytic infiltrate with routine immunohistochemistry. Ten patients (five male, five female, ages 4.5-21 years of age) had a thyroid carcinoma resection, six (three males and three females) with papillary carcinoma and four patients (two males and two females) with low-grade follicular carcinoma. Seven samples (one male had two cases with tumor) from patients who had a papillary carcinoma resection with tissue blocks available were identified (one patient had slides but no blocks), as were all four patients with a follicular carcinoma. The thyroid of all patients with a follicular carcinoma contained a lymphocytic infiltrate; only four of the seven papillary carcinoma samples had an associated lymphoid infiltrate. In all cases with a lymphoid infiltrate, the infiltrate was present in both lobes (both adjacent and separate from the tumor). B lymphocytes were present in the lymphoid infiltrate of three of four patients with follicular carcinomas and in 1 of 3 cases of papillary carcinomas. T cells were dispersed throughout all the tumors with lymphoid infiltrates. We conclude that pediatric follicular carcinomas have an associated lymphocytic infiltrate in the tumor and/or adjacent thyroid, more commonly than papillary carcinomas.