New subgrouping of small thyroid carcinomas.

Clinicopathologic findings on small thyroid carcinomas measuring 10 mm or less in diameter were analyzed in 78 thyroidectomied cases. The authors divided small thyroid tumors into two subgroups according to diameter: 0 less than or equal to 5 mm (classified as minute carcinoma) and 5 less than 0 less than or equal to 10 mm (classified as tiny carcinomas). Characteristics including sex, age, histologic type, extrathyroid invasion, and lymph node metastasis were examined in each subgroup. In patients with minute carcinoma, very few incidences of extrathyroid invasion and lymph node metastasis were found. However, these involvements, especially lymph node metastasis, were found more frequently in patients with tiny carcinoma. The incidence of cervical lymph node metastasis was 13% in minute carcinoma and 59% in tiny carcinoma. (P less than 0.01). These findings suggest the need for more careful observation and treatment of tiny carcinomas, especially with respect to lymph node metastasis. In accordance with World Health Organization (WHO) classification, the histologic types of thyroid carcinoma were classified into papillary and follicular carcinomas. The papillary carcinoma and follicular carcinoma ratios were compared between the two subgroups. The discovery rate of follicular carcinoma was significantly higher in minute carcinoma than in tiny carcinoma (P less than 0.005). This suggests that the papillary carcinoma/follicular carcinoma ratio (p/f) increases as the size of the carcinoma increases, and that follicular carcinoma is the "seed," or initial form, of thyroid cancer. The female-male ratio in small thyroid cancer suggests that there is no sex difference in carcinogenesis but that there is more probability for cancer development in the thyroid in women.