Changing Incidence of Breast Cancer in Japanese-American Women2

Mortality studies for the period around 1950 and 1960 showed breast cancer mortality rates of Japanese-American women only slightly above levels prevailing in Japan, though other site-specific cancer risks had shifted more markedly toward levels of white Americans. The Third National Cancer Survey of 1969–71 reveals that breast cancer risks for Japanese-American women in the San Francisco-Oakland metropolitan area closely approached those for whites. This upward shift occurred among both the Nisei (second generation) and the Issei (immigrant generation). The contribution of the Issei to the increased rates was substantial but somewhat less than that of the Nisei. Although Japanese and Polish migrants arrived in the United States about the same time, and both were mainly of rural origin, only the Polish women demonstrated a substantially increased risk of breast cancer by 1950. Japanese migrants may have retained their traditional culture longer, and when the strong upward shift in breast cancer risk occurred, it did so among Japanese-American women potentially exposed to a new culture and environment at preadult and early adult ages.