A new study finds 18 percent of smokers with lung cancer continue to smoke even after they have been diagnosed.

HealthDay reports that the study, sponsored by the U.S. National Cancer Institute, found that 25 percent of family members caring for patients with lung cancer kept on smoking.

Study lead author, Kathryn E. Weaver, said that lung cancer patients may continue to smoke because they believe it’s too late to quit smoking once they’re diagnosed. “There are benefits to be gained by quitting that have important implications for survival, response to treatments, and quality of life,” she told HealthDay. She noted that continuing to smoke increases the chance of developing a secondary cancer and can interfere with treatment.

Weaver said the findings show that lung cancer patients and their families need help in quitting smoking through family support, counseling and medication. The study was published in Cancer Epidemiology, Biomarkers & Prevention.