Reduced cancer risk seen after 10 years since quitting smoking

Sustained smoking cessation is associated with reduced cancer risk after 10 years since smoking cessation, according to a study published online in JAMA Network Open.

Eunjung Park, Ph.D., from the National Cancer Center Graduate School of Cancer Science and Policy in Goyang, South Korea, and colleagues examined the time course of cancer risk according to the time elapsed since smoking cessation in a retrospective cohort study involving 2,974,820 Korean participants aged 30 years and older.

The researchers confirmed 196,829 cancer cases during a mean follow-up of 13.4 years. Complete quitters had a lower risk for cancer compared with continuous smokers, with hazard ratios of 0.83 for all cancer sites, and 0.58, 0.73, 0.86, and 0.80 for lung, liver, stomach, and colorectum, respectively.

The risk for cancer was slightly elevated for the 10 years following quitting versus continued smoking and then decreased over time; after 15 or more years, the risk reached 50 percent of that associated with continued smoking.

The risk for lung cancer decreased three years earlier than that of other cancer types, and a larger relative reduction was seen. A greater reduction in lung cancer risk was seen in association with quitting before age 50 years compared with age 50 years or older (hazard ratios, 0.43 and 0.61, respectively).

"Our findings emphasize the significance of promoting smoking cessation, offering appropriate support and resources for sustained cessation, and encouraging cessation at an early age to reduce the risk of cancer," the authors write.