It is known that in cancer patients and survivors, there is evidence that continued cigarette smoking causes adverse health outcomes, including, but not limited to, increased mortality and an increased risk for second cancers caused by smoking. Quitting smoking improves the prognosis of cancer patients. The risk of dying could be lowered by 30–40% by quitting smoking at the time of diagnosis. In cancer patients and survivors, the evidence also suggests that there may be a causal relationship between cigarette smoking and (1) the risk of recurrence, (2) poorer response to treatment, and (3) increased treatment-related toxicity. More studies are needed to prove this.
U.S. Department of Health and Human Services. The Health Consequences of Smoking – 50 years of Progress: A Report of the Surgeon General. Atlanta, GA. Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2014, pages 323-325.