Long term smokers increase their spouses’ risk of developing lung cancer by more than 20%, according to a new report.

Occupational exposure to secondary smoke increases the likelihood of developing the disease by a similar amount, says the report, which is being published in the International Journal of Cancer and was published online on 10 December 2003 ahead of print publication (see "Early View" on www3.interscience.wiley.com/). "This pooled analysis of two large studies of second-hand smoke and lung cancer provides firm evidence for a dose-response relationship between lung cancer risk and duration of exposure to second-hand smoke for the three main sources of exposure spousal, workplace and social," wrote the authors of the international study, which was funded by the Department of Health, the US National Cancer Institute, the European Commission, and other agencies. "It provides more precise estimates of the effect of second-hand smoke on lung cancer risk in non-smokers from all sources than those previously obtained in individual studies and emphasises the importance of protecting non-smokers from second-hand smoke." The aim of the study, say the authors, was to obtain precise and valid estimates of the risk of people who had never smoked developing lung cancer after exposure to second-hand smoke. Pooled analysis of data from two large case-control studies was based on 1263 patients with lung cancer who had never smoked, and 2740 population and hospital controls recruited from the United Kingdom, the United States, Germany, Italy, Sweden, France, Spain, and Portugal. "Spousal exposure" to second-hand smoke was defined as ever having a spouse who smoked any tobacco product while living together. Those defined as having "never smoked" were those who had smoked fewer than 100 cigarettes in their lives or the equivalent in other tobacco products. The study used an upper age limit of 79. The researchers calculated the odds ratios for developing lung cancer for "ever-exposure" to spousal exposure and the duration of exposure to second-hand smoke from spouse, workplace, and social sources. The odds ratio for developing lung cancer for those ever exposed to spousal smoking was 1.18 (95% confidence interval 1.01 to 1.37) and for those with long term spousal exposure was 1.23 (1.01 to 1.51). For those ever exposed to smoking in the workplace, the odds ratio was 1.16 (0.99 to 1.36) and for those with long term exposure was 1.27 (1.03 to 1.57). Similar results were obtained for exposure in social settings and for exposure from combined sources. The results also show an increased risk of both adenocarcinoma and squamous and small cell carcinomas from all three sources of exposure. The authors, who found no evidence of confounding by employment in high risk occupations, education, or low consumption of vegetables, say that the risk figures probably underestimate the true risk. "The implications of reducing exposure to second-hand smoke go beyond the prevention of lung cancer in non-smokers, since such measures to reduce exposure to second-hand smoke also result in a decreased opportunity for smoking among active smokers and a subsequent reduction in active smoking levels," they say.

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