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Am J Epidemiol. 1999 Sep 15;150(6):561-7.

Breast cancer and oral contraceptive use in Asian-American women.

Author information

1
Department of Preventive Medicine, University of Southern California/Norris Comprehensive Cancer Center, Los Angeles 90033-0800, USA.

Abstract

Breast cancer incidence has historically been 4-7 times higher in the United States than in Asia. A previous study by the authors in Asian-American women demonstrated a substantial increase in breast cancer risk in women who migrated from Asia to the United States, with the risk almost doubling during the first decade after migration. Increased use of oral contraceptives soon after migration to the United States could possibly explain this rapid rise in risk. In a population-based case-control study of Chinese, Filipino, and Japanese-American women, aged 20-55 years, who lived in San Francisco-Oakland, California; Los Angeles, California; and Oahu, Hawaii during 1983-1987, 597 cases (70% of those eligible) and 966 controls (75%) were interviewed. Controls were matched to cases on age, ethnicity, and area of residence. Oral contraceptive (OC) use increased with time since migration; 15.0% of Asian-born women who had been in the West <8 years, 33.4% of Asian-born women who had been in the West > or =8 years, and 49.6% of Asian women born in the West had ever used OCs. However, duration of OC use (adjusted for age, ethnicity, study area, years since migration, education, family history of breast cancer and age at first full-term birth) was not associated with increased risk of breast cancer. Moreover, neither OC use before age 25 years nor before first full-term birth was associated with increased risk. Results were unchanged when restricted to women under age 45 years or under age 40 years. After adjustment for duration of OC use, women who had been in the United States > or =8 years were still at almost twice the risk of breast cancer compared with women who had been in the United States 2-7 years. This study suggests that OC use cannot explain the elevated risk observed in Asian women who migrated to the United States > or =7 years ago.

PIP:

The relationship between oral contraceptive (OC) use and breast cancer was investigated among Asian-American women. A population-based case-control study of Chinese, Japanese, and Filipino women, ages 20-25 years were interviewed. Results showed that women who had been in the West for 2-7 years had the lowest prevalence of use. About 15.0% were OC users, and 1.4% had been OC users for more than 5 years. Asian-Americans born in the West had the highest prevalence of OC use. However, there were only slight differences of OC use among women living in rural or urban areas while in the East. An inverse association is shown between the duration of OC use and breast cancer among migrants more than 8 years ago. There were no increased risks associated with the use of OC and the duration of OC use. Women who started using OC at an early age were not associated with an increased risk of breast cancer and with a decreased risk at the very onset of use (age 21 years). Recent OC use (last OC use during last 5 years) was not associated with an increased risk of breast cancer. Consequently, women who had been in the US more than 8 years were at almost twice the risk of breast cancer [odds ratio (OR) = 0.67] as women who had been in the country 2-7 years (OR = 0.34). This study suggests that OC use cannot explain the elevated risk observed in Asian-American women who migrated more than 7 years ago.

PMID:
10489994
[Indexed for MEDLINE]

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