Smoking during first pregnancy and breast cancer: a case-control study using Washington State registry data

To examine whether smoking during first pregnancy, a time of potential vulnerability to tobacco mutagens, is associated with breast cancer.

We conducted a nested case-control study within a cohort of Washington State residents with first deliveries during 1984-1999, identified in birth and fetal death records. Linkage to population-based cancer registry data identified 1,099 women in the cohort aged 65 years and younger diagnosed with breast cancer in 1985-2000. Controls (N=10,922) were matched by year and age of first delivery, race/ethnicity, and birth outcome. Maternal smoking and other variables characterizing the pregnancy were obtained from birth and fetal death records. Conditional logistic regression was used to analyze the data.

The adjusted risk ratio for breast cancer was 0.8, 95% confidence interval 0.7-0.9, among women who smoked during their pregnancy compared with similar women who did not smoke. When the sample was restricted to known state residents at the time of the matched case's diagnosis, there was no association (risk ratio 1.0; 0.8-1.1).

Our results do not suggest that cigarette smoking during first pregnancy increases the risk of breast cancer.