Gram IT, Wiik AB, Lund E, et al. - In a population of never-smoking women, the outcomes imply that 1 in 14 breast cancer cases could have been avoided in the absence of second-hand smoke (SHS) exposure from parents during childhood. As per the findings, the cancer burden attributable to SHS may be underestimated.

• In this study, 2,185 women developed invasive breast cancer, confirmed by histology during a mean follow-up of 19.8 (6.8) years.

• It was shown that women exposed to SHS from parents during childhood had an 11% higher (95% CI: 1.02–1.22) risk of breast cancer in comparison with those who were not.

• There was no difference for estrogen (P heterogeneity = 0.31) and progesterone (P heterogeneity = 0.95) receptor status.

• Results showed that for women exposed, the attributable fraction was 10.3% (95% CI: 1.8–18.0), whereas the population attributable fraction of breast cancer was 7.0% (95% CI: 1.0–13.0).