Women who smoke before or after a diagnosis of breast cancer have a significantly higher risk for death from breast cancer, respiratory tract cancers, and other causes than never smokers or quitters, follow-up results of a population-based prospective observation study show.

Among a subcohort of 4,562 women from the ages of 20 to 70, those who were active smokers within 1 year of a breast cancer diagnosis had a 25% greater risk for death from breast cancer, 14-fold higher risk for death from respiratory cancer, 6-fold risk for death from other respiratory diseases, and 2-fold higher risk for death from cardiovascular disease, found Dr. Michael N. Passarelli of the University of California, San Francisco, and his colleagues.

“Our study reinforces the importance of cigarette smoking cessation in women with breast cancer. For the minority of breast cancer survivors who continue to smoke after their diagnoses, these results should provide additional motivation to quit,” they write (J Clin Oncol. 2016 Jan 25. doi: 10.1200/JCO.2015.63.9328).

The investigators studied a cohort of 4,562 women who had taken part in the Collaborative Breast Cancer and Women’s Longevity Study, conducted in Massachusetts, New Hampshire, and Wisconsin. The study enrolled 20,691 women diagnosed from 1988 through 2008 with incident localized or regional invasive breast cancer.

The investigators re-contacted 4,562 participants a median of 6 years after their diagnosis. For women who reported smoking after breast cancer diagnosis, they calculated survival from the date of return of the questionnaire to the date of death or the end of follow-up.

The authors also created pre- and post-diagnosis proportional hazard regression models controlling for body mass index, education, parous status, age at first birth, menopausal status, family history of breast cancer, use of post-menopausal hormones, alcohol consumption, and the number of years between date of diagnosis and return of the study questionnaire.

For women who reported being active smokers within 1 year before a breast cancer diagnosis, hazard ratios (HR) for death from various causes were as follows (all statistically significant as shown by confidence intervals): breast cancer, HR 1.25; respiratory cancer, HR 14.48; other respiratory disease, HR 6.02; cardiovascular disease, HR 2.08.

For the 434 women (10%) who reported active smoking after diagnosis, the HR for breast-cancer death vs. never smokers was 1.72. Compared with women who continued to smoke, women who quit smoking after diagnosis had a lower risk for both breast-cancer death (a non-significant trend) and respiratory-cancer deaths (HR 0.39).