[The incidence of breast cancer in Niigata Prefecture].

The number of operations, regarded as the incidence, of breast cancer in Niigata Prefecture between 1972 and 1983 was surveyed. The age-adjusted incidence rate of female breast cancer in Niigata Prefecture has increased from 12.2 (per 100,000) to 21.1 (per 100,000) during the past 10 years, although the age-adjusted mortality rate has increased only slightly, from 3.7 to 4.2 (per 100,000) during that time. The age-adjusted incidence rate also increased in the middle-aged (61%) and elderly (41%) group, incidence increased only in the elderly group (74%). It has recently been reported that the aging phenomenon of breast cancer in Japan shows a Western-type tendency. In this paper, however, this phenomenon was considered to be due merely to the increase (24%) in the population of the elderly.