Risk of childhood cancer and adult lung cancer after childhood exposure topassive smoke: A meta-analysis

We identified more than 30 studies on the association between exposure to m aternal tobacco smoke during pregnancy and cancer in childhood. We combined their results in meta-analyses based on a random effects model. The result s of the meta-analyses suggest a small increase in risk of all neoplasms [r elative risk (RR) 1.10; 95% confidence interval (CI), 1.03-1.19; based on 1 2 studies], but not of specific neoplasms such as leukemia (RR 1.05; CI, 0. 82-1.34; 8 studies) and central nervous system tumors (RR 1.04; CI, 0.92-1. 18; 12 studies). Results for other specific neoplasms were sparse, but the available data did not suggest a strong association for any type of tumor. No clear evidence of dose response was present in the studies that addresse d this issue. The results on exposure to maternal tobacco smoke before or a fter pregnancy are too sparse to allow a conclusion. The results on exposur e to paternal tobacco smoke suggest an association with brain tumors (RR 1. 22; CI, 1.05-1.40; based on 10 studies) and lymphomas (RR 2.08; CI, 1.08-3. 98: 4 studies). The data are too sparse for the other neoplasms, although t he results of a few recent large studies are compatible with a weak carcino genic effect of paternal smoke. For exposure from either maternal or patern al smoke, bias and confounding cannot yet be ruled out. Further studies are needed to confirm the hypothesis that parental tobacco smoke, from the fat her in particular, is a risk factor of childhood cancer. Results on the ris k of lung cancer in adulthood and childhood passive smoking exposure are av ailable from 11 studies: they do not provide evidence of an increased risk (summary RR 0.91; CI, 0.80-1.05).