Birth size and breast cancer risk among young California-born women

Evaluate the risk of breast cancer associated with birth size among young California-born women.

Invasive breast cancer cases diagnosed 1988-2004 among women born in California during the 1960s were identified from the California Cancer Registry. Breast cancer cases (n = 3,712) were linked to their California birth records. Controls (n = 8,615) were randomly selected from California birth records for women, frequency matched to cases by birth year. Odds ratios (ORs) and 95% confidence intervals (95% CI) were estimated from unconditional logistic regression.

The adjusted OR for breast cancer associated with the highest category of birth weight (≥4,000 g) was 1.12 (95% CI 0.89-1.41), p-trend = 0.02. The adjusted OR for the highest category of birth length (>20 inches) was 1.13 (95% CI 1.02-1.25), p-trend = 0.02. These relationships appeared to be confined to cases with estrogen receptor positive (ER+) tumors (p-trend ≤0.01) or progesterone receptor positive (PR+) tumors (p-trend ≤0.02). No significant associations were found among cases with ER or PR negative tumors.

Our results confirm previous findings of elevated breast cancer risk associated with increases in birth size. These risks may be confined to ER+ and PR+ tumors, highlighting the potential mechanistic role of sex steroid hormonal pathways.