Sustained smoking cessation may significantly lower risk of cancer after ten years since quitting: JAMA

In the population-based cohort study, the cancer risk showed a slightly higher value for 10 years following quitting versus with continued smoking, and then decreased gradually, reaching 50% of the risk associated with continued smoking after 15 years or more.

"There was a decrease in lung cancer risk 3 years earlier than that of other cancer types, with a larger relative reduction," the researchers reported in their study published in JAMA Network Open.

Furthermore, smoking cessation at any age helped reduce the cancer risk, and early cessation before middle age, especially for lung cancer, exhibited a substantial risk reduction, the study stated.

Tobacco smoking is linked with an increased risk of various cancers, and previous studies have shown that smoking cessation may reduce cancer risks. However, there is no clarity on how many years of smoking cessation are required to significantly reduce cancer risk. Therefore, it is essential to investigate the association of smoking cessation with cancer.

Against the above background, Eunjung Park, National Cancer Center Graduate School of Cancer Science and Policy, Goyang, Republic of Korea, and colleagues investigated the time course of cancer risk according to the time elapsed since smoking cessation and the benefits of smoking cessation according to the age at quitting.

The study included Korean participants aged 30 years and older who underwent two or more consecutive health examinations under the National Health Insurance Service since 2002 and followed up until 2019.

Of the 2,974,820 participants, 58.1% were men (mean age, 43.1 years), and 41.9% were women (mean age, 48.5 years). Over a mean follow-up of 13.4 years, 196,829 cancer cases were confirmed.

Exposures included (!) time-updated smoking status based on biennial changes in smoking status, defined as transient quitters, continuous smokers, complete quitters, relapsed quitters, and never smokers; (2) smoking cessation duration, defined as years since quitting; and (3) categorical variable for age at quitting.

Using the cancer registry data, the researchers ascertained the primary cancer.

The study led to the following findings:

• Compared with continuous smokers, complete quitters had a lower risk of cancer, with HRs of 0.83 for all cancer sites, 0.73 for the liver, 0.58 for the lung, 0.86 for the stomach, and 0.80 for the colorectum.
• The cancer risk exhibited a slightly higher value for 10 years after quitting compared with continued smoking, and then it decreased over time, reaching 50% of the risk associated with continued smoking after 15 or more years.
• Lung cancer risk decreased three years earlier than that of other cancer types, with a larger relative reduction.
• There was a significant reduction in the cancer risk regardless of quitting age.
• Quitting before the age of 50 years was associated with a greater reduction in lung cancer risk (HR, 0.43) compared with quitting at age 50 years or later (HR, 0.61).

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

Reference:

Park E, Kang H, Lim MK, Kim B, Oh J. Cancer Risk Following Smoking Cessation in Korea. JAMA Netw Open. 2024;7(2):e2354958. doi:10.1001/jamanetworkopen.2023.54958