Characteristics of the Japanese histological classification for breast cancer: correlations with imaging and cytology.

The Japanese histological classification of breast cancer is a unique classification that was published as the 2nd edition of the General Rules for Clinical and Pathological Recording of Breast Cancer in 1971. According to this classification, breast cancers are divided into three subgroups: noninvasive, invasive, and Paget's disease. Invasive carcinomas are further divided into two groups: invasive ductal carcinomas (IDCs) and special types. IDCs are the most common types, representing 70-80 % of all breast cancers, and most of them correspond to invasive carcinoma-not special type-according to the latest WHO classification (4th edition). In particular, IDCs are subdivided into three subgroups as follows: (1) papillotubular carcinoma, which is characterized by the projection of papillae into spaces, and includes cribriform and comedo patterns; (2) solid-tubular carcinoma, which is a solid cluster of cancer cells with expansive growths that form relatively sharp borders; and (3) scirrhous carcinoma, which grows in a scirrhous manner characterized by cancer nests or cells accompanied by marked fibrosis. The concept of subclassification originated in Japan. The Japanese histological classification has taken on important roles since its publication, in particular for comparisons between histology and imaging or cytology.