Second hand smoke, age of exposure and lung cancer risk Free

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Introduction: Exposure to second hand smoke (SHS) has been identified as a risk factor for lung cancer for three decades. It is also known that the lung continues to grow from birth to adulthood when lung growth stops. We hypothesize that after adjusting for active cigarette smoking, if the exposure took place during the period of growth i.e. in the earlier part of life (0 to 25 years of age) the risk of lung cancer is greater compared to an exposure occurring after age 25.

Method: This study population of 1669 cases and 1263 controls is derived from a large ongoing case control study evaluating the molecular epidemiology of lung cancer, which began in 1992 at the Massachusetts General Hospital. Lung cancer cases were all histologically confirmed and the controls were the friends or spouses of cancer patients or other cardiothoracic surgery patients in the same hospital. Interviewer-administered questionnaires collected information on demographics, occupational exposures, and detailed smoking histories from each subject. Second hand smoke exposure was self-reported for three different activities (leisure, work and at home). We created variables that captured location of exposure and timing of first exposure with respect to a study participant’s age (0 - 25, >25 years of age). Multiple logistic regression was used to study the association between SHS exposure and lung cancer, adjusting for age, gender and active smoking variables.

Result: Median age (standard deviation) was 62 (12) years, males were 49%; 604 (21%) non smokers, 1464 (50%) ex smokers, 864 (29%) current smokers; median packyears (standard deviation) for ex and current smokers 39(37); early stage (stages I an II) 803 50%, adenocarcinoma 698 (42%), squamous 339 (21%), others 615 (37%). No exposure to SHS at work or leisure 212 (7%), one activity 727 (25%), or both 1993 (68%). Exposure to SHS between birth and age 25, 403 (14%), after age 25, 2529 (86%). Exposure at home was excluded from further analysis since there was little variability by outcome status (most subjects reported exposure from birth). For study participants that were exposed to SHS at both activities and compared to one or no activity, the adjusted odds ratio (AOR) for lung cancer was 1.30(1.08-1.57) when exposure occurred between birth and age 25 and 0.66(0.21-1.57) if exposure occurred after age 25 years. Respective results for nonsmokers were1.29 (0.82-2.02) and 0.87 (0.22-3.38), and current and ex smokers combined 1.28 (1.04-1.58) and 0.66 (0.15-2.85).

Conclusion: All individuals exposed to SHS have a higher risk of risk of lung cancer. Furthermore, this study suggests that subjects first exposed before age 25 have a higher lung cancer risk compared to those for whom first exposure occurred after age 25 years.

Grant Support

NIH Grants: CA74386 and ES00002.

Flight Attendant Medical Research Institute