Stage-specific breast-cancer incidence rates by age among Japanese and Caucasian women in Hawaii, 1960-1979

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Abstract
We have analysed the age- and stage-specific breast-cancer incidence rates of Japanese and Caucasian women in Hawaii for a 20-year period. A comparison of the 1192 Japanese and 1531 Caucasian patients by stage at diagnosis showed that Japanese women were likely to have breast cancer diagnosed at an earlier stage than Caucasian women, but this difference was statistically significant only after the menopause (ages 55+). We further found that for age 50-74, the age-specific ratios of Caucasian to Japanese incidence rates were least for in situ breast cancer, and successively greater for localized, regional and distant breast cancer. We interpreted this latter finding to be an indication that postmenopausal breast cancers in Japanese women have slower average growth rates than in Caucasian women. Such slower growth rates may explain the better breast-cancer survival among Japanese women after allowing for differences in stage, tumour size, histology, or treatment.