WashU Medicine Oct 9 2025 Around 25% of people with cancer in the U.S. are active smokers when they are diagnosed, and studies have found that many of them continue to smoke during treatment. This may be due in part to a common misconception - even among some doctors - that quitting won't help much if a person already has cancer, particularly if it's at an advanced stage. Now, a study led by Li-Shiun Chen, MD, a professor of psychiatry at Washington University School of Medicine in St. Louis,