Cancer risk reduced a decade after smoking cessation

For ex-smokers, the risk of cancer appears to significantly decrease 10 years after quitting, according to a study from Korea.

For the study, researchers reviewed the medical records of 2,974,820 adult Koreans (mean age 43.1 years, 58.1 percent men) who had undergone at least two health examinations under the National Health Insurance Service. Data on time-updated smoking status (ie, complete quitters, transient quitters, relapsed quitters, continuous smokers, and never smokers) and on duration of smoking cessation (defined as years since quitting) were collected.

The incidence of all-site cancer and cancer of the lung, liver, stomach, colon, and rectum was determined using data from the cancer registry. Cox proportional hazards regression model was applied in the analyses.

Of the participants, 58.1 percent were men (mean age 43.1 years) and 41.9 percent were women (mean age 48.5 years). A total of 196,829 cancer cases were documented over a mean follow-up of 13.4 years.

Compared with continuous smokers, complete quitters had a lower risk of all-site cancer (hazard ratio [HR], 0.83, 95 percent confidence interval [CI], 0.80–0.86), lung cancer (HR, 0.58, 95 percent CI, 0.53–0.62), liver cancer (HR, 0.73, 95 percent CI, 0.64–0.82), stomach cancer (HR, 0.86, 95 percent CI, 0.79–0.93), and colorectal cancer (HR, 0.80, 95 percent CI, 0.72–0.89).

There appeared to be temporary increase in the risk of cancer after quitting, but the risk decreased steadily after the 10-year mark. After 15 or more years of being smoke-free, the cancer risk dropped to 50 percent of the risk associated with continued smoking. Notably, lung cancer risk decreased 3 years earlier than that of other cancer types, with a larger relative reduction.

The benefit of smoking cessation on the risk of cancer was observed regardless of quitting age. Quitting before the age of 50 years was associated with a greater reduction in lung cancer risk (HR, 0.43, 95 percent CI, 0.35–0.53) compared with quitting at age 50 years and up (HR, 0.61, 95 percent CI, 0.56–0.66).