Men who continue smoking after a cancer diagnosis have significantly greater risk of death from any cause than did those who quit smoking at the time of diagnosis, according to findings from the prospective population-based Shanghai Cohort Study.
Of 1,632 men from that ongoing study who developed cancer after enrollment and who were eligible for the current analysis, 931 died during 25 years of follow-up, and 747 of those who died were smokers at the time of their cancer diagnosis. Of these smokers, 214 (29%) quit at the time of diagnosis, 197 (26%) smoked persistently after diagnosis, and 336 (45%) smoked intermittently after diagnosis.
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Men who continue smoking after a cancer diagnosis have significantly greater risk of death from any cause than did those who quit smoking at the time of diagnosis, according to findings from the study.
After the researchers adjusted for age at diagnosis, education, cumulative number of pack-years of prediagnosis smoking, cancer site, and treatment modalities, the risk of death was 76% greater in those who smoked persistently or intermittently after diagnosis, compared with those who quit at diagnosis, reported Dr. Li Tao of the Cancer Prevention Institute of California, Fremont, and her colleagues.
Median survival was 2.1 years after diagnosis for those who continued smoking, compared with 4.4 years for those who quit, the investigators said.
Using a time-dependent approach, and including all patients with cancer, the overall risk of mortality was 59% greater for smokers vs. nonsmokers after cancer diagnosis.
"When analyzed separately for cancer specific patients, the multivariate-adjusted hazard ratios of death for smoking relative to nonsmoking after cancer diagnosis were 1.92 for patients with lung cancer, 1.76 for patients with stomach cancer, 1.65 for patients with colorectal cancer, and 3.66 for patients with bladder cancer," the investigators wrote.
In a similar analysis that included only current smokers at cancer diagnosis, smoking after cancer diagnosis was associated with a 79% increase risk of death relative to nonsmoking after diagnosis for all patients.
"Among cancer-specific patients, the [hazard ratios] of death for smoking vs. nonsmoking after cancer diagnosis were 2.36 in patients with lung cancer, 1.63 in patients with stomach cancer, 2.31 in patients with colorectal cancer, 2.95 in patients with bladder cancer, 2.27 in patients with prostate cancer, and 1.34 in all other patient with cancer," the investigators said (Cancer Epidemiol. Biomarkers Prev. 2013;22:2404-11).
The Shanghai Cohort Study is investigating the association between lifestyle characteristics and cancer development in more than 18,000 middle-age or older men who were enrolled between Jan.1, 1986, and Sept. 30, 1989. Smoking status is ascertained via annual in-person interviews. Patients in the current analysis had a mean age of 68.8 years and were followed for a mean of 5.3 years after cancer diagnosis. They had a median survival time of 5.4 years after diagnosis.
The findings provide new information about smoking and cancer survival, the investigators said, noting that cancer is the leading cause of death among men in China, and the second leading cause of death among men in the United States.
Tobacco use is the most important recognized cause of cancer-related death, they said, adding that strong evidence demonstrates an association between smoking and cancer risk, and between improved health and smoking cessation.
The impact of smoking after a cancer diagnosis, however, has not been well studied, and existing data are conflicting, they noted.
The findings of the present study, which have important public health implications for cancer survivors, health care providers, and policy makers, underscore the importance of smoking cessation interventions – and the potential benefit of cessation on survival – in patients who are diagnosed with cancer, they said.
Although patients diagnosed with cancer are expected to "show great interest and motivation to quit smoking," many face physical, psychological, and social stress that impedes their ability to do so. Furthermore, only about 50% of smokers diagnosed with cancer in the United States receive formal smoking cessation counseling at diagnosis, during treatment, or during follow-up visits, they noted.
"Therefore, there is noticeable room for the improvement of self-managed or health care provider–assisted smoking cessation in the clinical setting of patients with cancer," they wrote, also noting that the message about inferior survival among those who continue smoking after a cancer diagnosis should be conveyed to patients and their families, and should be included in guidelines and evidence-based clinical practices.
This study has considerable strengths – such as knowledge of baseline smoking status and the prospective design. It also has limitations, including limited treatment data and inclusion of only patients who survived 1 or more years after cancer diagnosis.