Rates of breast cancer among Japanese-American and other Asian ethnic women are on the rise, researchers report, and a significant factor may be unhealthy eating and living habits adopted with time in the United States.

The analysis of breast cancer cases reported in Los Angeles County found a 6 percent annual increase in the incidence of the disease between 1993 and 1997 among Asian-American women. At the same time, the rate of breast cancer rose at a clip of less than 2 percent a year among white women, according to Dennis Deapen from the University of Southern California in Los Angeles and fellow researchers.

Asians of Japanese descent were the first of the Asian groups studied to migrate to Los Angeles County, where rates of breast cancer reflect national rates. The findings support previous studies indicating that Asian women who migrate to the United States have higher rates of breast cancer than their relatives who stay in their native country, and underscore the potential contribution of diet and lifestyle to breast cancer risk.

The United States has one of the highest breast cancer rates, with roughly 110 per every 100,000 women diagnosed with the disease each year. In Japan, the incidence of breast cancer more than doubled between 1960 and the late 1980s as people adopted more Western habits and tastes.
Japanese women today have fewer children, exercise less and are more prone to obesity than their grandmothers, for instance. A higher intake of dietary fat and lower intake of soy products, which contain plant-derived estrogens that may reduce a woman's risk of breast cancer, may also be contributing to increasing rates of breast cancer over the past several decades, researchers suggest.

"The rapid increase in breast cancer incidence rates in Japanese suggests a prominent role of exogenous and, therefore, potentially alterable factors," the authors conclude.
The results underscore the need for breast cancer screening and education among Asian Americans.

"It is possible that many physicians are unaware that the well-known low breast cancer risk among these women in past decades is no longer true and that breast cancer screening is as important as among white and African-American women," the report concludes in the latest issue of the International Journal of Cancer.

According to the study of women older than 50 years, the rate of breast cancer was highest among Japanese women, among whom there were 114 cases for every 100,000 women in 1997. During that year, the breast cancer incidence rate for Filipino women was 98 cases per 100,000; 51 cases per 100,000 for Chinese women; and 45 cases per 100,000 for Korean women.