[Up-to-date pathological diagnosis for breast cancer]

The number of breast cancer patients among Japanese women has been increasing, and one in fourteen women may develop breast cancer during their lifetime. Most cases of breast cancer occur in the terminal duct-lobular units, but their pathological features are quite heterogeneous. Thus, it is necessary to examine them pathologically, to establish appropriate adjuvant therapy for individual patients. In addition to determining the histological type, tumor size, tumor grade, lymphovascular invasion, node metastases, and surgical margin status (for breast-conserving surgery), we should clarify the biomarker status. Analyses of estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor 2 (HER2) are routinely performed currently, but strict quality control is strongly recommended, including pre-analytical issues. In addition, the Ki-67 labeling index has been employed as a marker to determine the indication for adjuvant chemotherapy for hormone receptor (ER/PgR)-positive, HER2-negative invasive carcinoma patients. The significance of PgR may alter, too. The threshold for the therapeutic indication may alter with the progress of pharmacology. The evidence-based data and expert consensus (i.e., St. Gallen international meeting consensus) may influence our daily practice. In this issue, we introduce the newest histological classifications (by the WHO and the Japanese Society of Breast Cancer) and the Japanese Breast Cancer Treatment Guideline. Several issues to be included in the pathology reports are examined, and the current status as well as future perspectives of biomarker analysis will be discussed.