Abstract B52: Racial/ethnic disparities in breast cancer among young women born in California

Introduction: This study was initiated to evaluate the relationship between breast cancer risk in young women and selected perinatal characteristics associated with prenatal estrogen exposures, including maternal age, maternal pre-eclampsia, twinning, infant birth order, infant birth weight, and gestational age at birth.

Methods: We conducted a population-based case control study among young women born in California. Invasive breast cancer cases diagnosed 1988–2004 were identified from the California Cancer Registry (CCR). Cases were restricted to women living in California at diagnosis who were born in the 1960s with either a California or unknown birthplace listed in the CCR. Probabilistic record linkage was used to link breast cancer cases to their California birth records. Population controls were selected from California birth records, frequency matched to cases 2:1 on year of birth. Controls were linked to death files to remove any women who died prior to the start of cancer follow-up. Data on birth characteristics and race were extracted from the birth records. Odds ratios (ORs) and 95% confidence intervals were calculated for race and for each of the perinatal characteristics of interest. Stratified analyses were conducted to evaluate whether the relationship between perinatal factors and breast cancer varied by race.

Results: Overall, 50% of eligible cases were linked to a California birth record (77% success for CCR records with California birthplaces; 38% for records with birthplace = unknown). Analyses were conducted on a total of 3,799 cases of breast cancer and 8,789 controls. Our study population was very young (age range for cases at diagnosis = 22 to 44 years) and predominantly White (87%), but included substantial numbers of Blacks (n=1,207) and Asian/Pacific Islanders (APIs) (n=422). Compared to young White women, young Black women (OR=1.5, 95% CI: 1.3 – 1.7) and young API women (OR = 1.6, 95% CI: 1.3 – 2.0) had higher risks of breast cancer. Although based on relatively small numbers, the elevated risk of breast cancer among API women was universally observed among Japanese, Filipina, and Chinese women. Our examination of the risk of breast cancer associated with the perinatal characteristics of interest showed similar associations among all races, with the exception of birth weight and twinning which appeared to be associated with an increased breast cancer risk among Blacks but not among any other racial groups examined.

Conclusion: Our finding of an elevated risk of breast cancer among young Black women is consistent with published reports based on cancer surveillance data. Our finding of an increased risk of breast cancer among API women is not consistent with the generally lower observed incidence of breast cancer reported among these women compared with White women in this age group. This may be due to the fact that a large proportion of API women in the US are foreign-born, while all of the women in our study were born in California. Future investigations into breast cancer risk among young women are warranted and should take into account nativity. Our finding of differing risks associated with perinatal characteristics between Black and White women underscores the importance of examining these factors in diverse populations.