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Whether women are more susceptible than men to smoking-related lung cancer has been a topic of controversy. To address this question, we compared risks of lung cancer associated with smoking by sex. Altogether, 585,583 participants from 3 Norwegian cohorts (Norwegian Counties Study, 40 Years Study, and Cohort of Norway (CONOR) Study) were followed until December 31, 2013, through linkage of data to national registries. We used Cox proportional hazards models and 95% confidence intervals to estimate risks. During nearly 12 million person-years of follow-up, 6,534 participants (43% women) were diagnosed with lung cancer. More men than women were heavier smokers. Compared with never smokers, male and female current smokers with ≥16 pack-years of smoking had hazard ratios for lung cancer of 27.24 (95% confidence interval (CI): 22.42, 33.09) and 23.90 (95% CI: 20.57, 27.76), respectively (P for heterogeneity = 0.30). In contrast, for current smokers, in a model with pack-years measured continuously, men had a hazard ratio of 1.43 (95% CI: 1.39, 1.48) and women a hazard ratio of 1.64 (95% CI: 1.57, 1.71) for each 10-pack-year increment of smoking (P for heterogeneity < 0.01). Our results suggest that women have an increased susceptibility to lung cancer compared with men, given the same lifetime smoking exposure.

Recent studies have found that the risk of death continues to increase among female smokers, as compared with women who have never smoked. We wanted to examine the effect of smoking on all-cause and cause-specific mortality and calculate the corresponding population attributable fraction (PAF) of mortality in the Norwegian women and cancer study; a nationally representative prospective cohort study. We followed 85,320 women, aged 31–70 years, who completed a questionnaire in 1991–1997, through linkages to national registries through December 2008. Questionnaire data included information on lifestyle factors, including lifetime history of smoking. Poisson regression models were fitted to estimate relative risks (RRs) with 95 % confidence intervals (CIs) adjusting for age, birth cohort, education, postmenopausal status, alcohol consumption and body mass index, all at enrollment. During a mean follow-up time of 14 years 2,842 deaths occurred. Compared with that of never smokers, current smokers had a mortality rate that was double (RR = 2.34; 95 % CI 2.13–2.62) from deaths overall, triple (RR = 3.30; 95 % CI 2.21–4.82) from cerebrovascular disease and myocardial infarction (RR = 3.65; 95 % CI 2.18–6.15), 12 times (RR = 12.16; 95 % CI 7.80–19.00) from lung cancer and seventeen times (RR = 17.00; 95 % CI 5.90–48.78) from chronic obstructive pulmonary diseases. The PAF of mortality due to smoking was 34 % (CI 30–39). In summary, one in three deaths among middle aged women in Norway could have been prevented if the women did not smoke. More middle-aged women, than ever before, are dying prematurely due to smoking in Norway.

Background: Smoking is a recently established risk factor for colon cancer. We wanted to explore the hypothesis that women may be more susceptible to smoking-attributed colon cancer than men as one of the possible explanations for the high colon cancer risk of Norwegian women., Methods: We followed 602,242 participants aged 19 to 67 years at enrollment in 1972-2003, by linkage to national registries through December 2007. We used Cox proportional hazard models to estimate HRs and 95% confidence intervals (CI)., Results: During a mean follow-up of 14 years, altogether 3,998 (46% women) subjects developed colon cancer. Female ever-smokers had a 19% (HR = 1.19, 95% CI = 1.09-1.32) and male ever-smokers an 8% (HR = 1.08, CI = 0.97-1.19) increased risk of colon cancer compared with never smokers. For all the four dose-response variables examined, female ever-smokers in the most exposed category of smoking initiation, (HR = 1.48, 95% CI = 1.21-1.81), of daily cigarette consumption (HR = 1.28, 95% CI = 1.06-1.55), of smoking duration (HR = 1.47, 95% CI = 1.11-1.95), and of pack-years of smoking (HR = 1.33, 95% CI = 1.11-1.57) had a significantly increased risk of more than 20% for colon cancer overall and of more than 40% for proximal colon cancer, compared with never smokers. A test for heterogeneity by gender was statistically significant only for ever smoking and risk of proximal colon cancer (Wald χ(2), P = 0.02)., Conclusions: Female smokers may be more susceptible to colon cancer and especially to proximal colon cancer than male smokers., Impact: Women who smoke are more vulnerable to colon cancer than men.

Objective: The association between cigarette smoking and colorectal cancer (CRC) is still not established. In 2002, Norwegian women had the second highest incidence of CRC in the world. A large proportion of Norwegian women are ever smokers. We examined the association between cigarette smoking and CRC incidence among Norwegian women., Methods: We followed 68,160 women, aged 30-69 years, from the Norwegian Women and Cancer Study who completed a questionnaire in 1996 or 1998 by linkages to national registers through 31 December 2005. Rate ratios (RRs) and 95% confidence intervals (CIs) were estimated by fitting Cox proportional hazard models. Subsequently, we estimated the population attributable fraction., Results: Altogether, 425 incident cases of primary, invasive CRC were identified. Ever smokers had a 20% increased risk of CRC (RR = 1.2; 95% CI = 1.0-1.5), a 30% increased risk of colon (RR = 1.3; 95% CI = 1.0-1.7), and a 10% increased risk of rectal (RR = 1.1; 95% CI = 0.7-1.5) cancer compared to never smokers. The population attributable fraction was estimated to be 12% which indicated that approximately one in eight of the CRC cases could have been prevented at a population level., Conclusion: Our results support the hypothesis that cigarette smoking is a preventable cause of CRC among women.

Studies regarding the association between smoking and risk of epithelial ovarian cancer (EOC) are inconsistent. The purpose of this study was to examine the association between smoking and EOC, overall and according to invasiveness and histological subtype in a cohort of women with a high proportion of smokers at enrollment. We followed 103,081 women, aged 30-50 years in 1991/1992, from the Norwegian-Swedish Women's Lifestyle and Health cohort. The women completed a questionnaire on personal characteristics and exposures at enrollment and were subsequently followed with linkages to national registers through December 31, 2004. We used Cox proportional hazard regression models to estimate hazard ratio (RR) of EOC with 95% confidence intervals (CIs) associated with different measures of smoking exposures adjusting for confounding variables. Altogether 343 [241 (70%) invasive and 102(30%) borderline] incident EOC cases were identified. Former [HR = 2.2(95% CI 1.0-4.7)] and current [HR = 2.7(95% CI 1.2-5.7)] smokers had a more than doubling in risk for borderline tumors compared to never smokers. Women who had smoked for more than 20 years had 3 times [HR = 3.1(95% CI 1.5-6.7)] the risk of borderline tumors compared to never smokers. A test for trend according to smoking status was almost significant for mucinous tumors (p-trend = 0.05). A significant dose response relationship was found according to smoking intensity [pack-years; (0-9, 0-14, >or= 15)] and duration [number of years; (0-10, 11-20, >or= 20)] for borderline and serous tumors (p-trends < 0.05). In conclusion, smoking may increase the risk of borderline EOC., ((c) 2007 Wiley-Liss, Inc.)

The purpose of this randomized controlled trial was to examine if an adjunct research project to a breast cancer screening programme would affect the high programme attendance. Women residing in the municipality of Tromsø aged 55 years or older, scheduled to receive an invitation letter to their first screening round in the Norwegian Breast Cancer Screening Programme during our 15-week recruitment period, were eligible. We randomly selected up to 25 invitees per screening day to receive a mailed request to participate in the research project named the Tromsø Mammography and Breast Cancer study. These women constituted the study arm, while the remaining eligible invitees served as the control arm. The attendance rate to the screening programme was 80.1% among the 253 women in the study arm and 74.8% among the 397 women in the control arm (P = 0.09). Our trial finds no effect on the high attendance to the breast cancer screening programme indicating that cancer screening programmes might be suitable settings for adjunct research projects.

Objective: To examine the effect of smoking on breast cancer risk in a large population-based cohort of women, many of whom started smoking as teenagers., Methods: We followed 102,098 women, ages 30 to 50 years, completing a mailed questionnaire at recruitment to the Norwegian-Swedish Cohort Study in 1991/1992, through December 2000. We used Cox proportional hazard regression models to estimate relative risk (RR) of breast cancer associated with different measures of smoking initiation, duration, and intensity adjusting for confounding variables. We conducted analyses on the entire study population, among women who had smoked for at least 20 years, among nondrinkers, and separately for each country., Results: Altogether, 1,240 women were diagnosed with incident, invasive breast cancer. Compared with never smokers, women who smoked for at least 20 years and who smoked 10 cigarettes or more daily had a RR of 1.34 (95% CI, 1.06-1.70). Likewise, those who initiated smoking prior to their first birth (1.27, 1.00-1.62), before menarche (1.39, 1.03-1.87), or before age 15 (1.48, 1.03-2.13) had an increased risk. In contrast, women who had smoked for at least 20 years, but started after their first birth, did not experience an increased breast cancer risk. The increased RR associated with smoking was observed among nondrinkers of alcohol, women with and without a family history of breast cancer, premenopausal and postmenopausal women, and in both countries., Conclusion: Our results support the notion that women who start smoking as teenagers and continue to smoke for at least 20 years may increase their breast cancer risk.