Pathology of breast cancer: present and prospect in Japan.

Breast cancer among Japanese females is characterized by its relatively low incidence and better prognosis than among Caucasian females. The annual mortality due to breast cancer among Japanese is about one-fifth that among Caucasians. Comparison of case distribution by histological type indicates that the ratio of well-differentiated carcinoma is slightly higher among Japanese, while the ratio of poorly differentiated carcinoma is slightly higher among Caucasian females. It is noteworthy that the incidence of in situ and invasive lobular carcinoma among Japanese is much lower than among Caucasian females. The age distribution shows that breast cancer is more frequent among middle-aged females in Japan, but more common among aged females in the West. Breast cancer among Japanese females shows a better prognosis than among Caucasian females as a whole, even with equal tumor size and lymph node metastasis. As mentioned above, the morbidity and mortality rates of breast cancer among Japanese females are very low, but recently, both morbidity and mortality rates in Japan have been steeply increasing. For example, the mortality rate of breast cancer in Japan almost doubled during the past 20 years. Moreover, biological behavior of breast cancer among Japanese females has been recently changing. Time-trend data clearly indicate that breast cancer in Japan in the future will be much more like that in the West, and nowadays it is already westernizing.