A Cohort Study of thyroid cancer and other thyroid diseases after the Chornobyl accident - Pathology analysis of thyroid cancer cases in Ukraine detected during the first screening (1998-2000)

BACKGROUND. The Ukrainian American Cohort Study evaluated the risk of thyroid disorders in a group of individuals who were younger than age 18 years at the time of the Chornobyl (Chernobyl) accident. In this article, the authors describe the pathology of thyroid carcinomas detected in the first screening. METHODS. From 1998 to 2000, 13,243 individuals completed the first cycle of screening examinations. Eighty patients underwent surgery between 1998 and 2004. Intraoperative and postoperative pathologic studies were performed at the Institute of Endocrinology and Metabolism, Kyiv. RESULTS. Pathologic analysis revealed 45 thyroid carcinomas, including 43 papillary thyroid carcinomas (PTCs) (95.6%) and 2 follicular thyroid carcinomas (FTCs) (4.4%). TNM classification (5th edition) of the PTCs included 8 T1 tumors (18.6%), 16 T2 tumors (37.2%), and 19 T4 tumors (44.2%). Fifteen PTCs (34.9%) were N1a,N1b, and 3 PTCs (7.0%) were M1. Among the PTCs, 8 exhibited the classical papillary histologic pattern (18.6%), 14 exhibited a follicular histologic pattern (32.6%), 5 exhibited a solid histologic pattern (11.6%), and 16 exhibited a mixed histologic pattern (37.2%). Both FTCs had a microfollicular-solid structure. Eleven of 20 cohort members who underwent surgery before the first screening had PTCs. Regional metastases (63.6%) and distant metastases (18.2%) were more common in this group. CONCLUSIONS. Multifocal growth, lymphatic and blood vessel invasion, extrathyroid spread, and regional and distant metastases were more frequent in less differentiated PTCs (> 30% solid structure). Small carcinomas (<= 10 mm) comprised 23.3% of PTCs, and most of those (8 of 10 small carcinomas; 80%) were of the papillary-follicular subtype and therefore were more differentiated. The solid subtype of PTC was associated with shorter latency, especially in individuals who were diagnosed before the first screening. The histology of post-Chornobyl cancers is changing with time.