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Smoking cessation was associated with a reduced cancer risk in the long run, particularly when quitting was sustained and occurred prior to middle age, a large population-based study from Korea found.

Over a mean 13 years follow-up, smokers who completely quit had a 17% lower risk of any cancer compared with people who continuously smoked (HR 0.83, 95% CI 0.80-0.86), according to findings from Jin-Kyoung Oh, PhD, of the National Cancer Center in Gyeonggi, Korea, and colleagues.

Complete quitters had lower cancer risk when it came to several different tumor types as well:

• Lung cancer: HR 0.58 (95% CI 0.53-0.62)
• Liver cancer: HR 0.73 (95% CI 0.64-0.82)
• Stomach cancer: HR 0.86 (95% CI 0.79-0.93)
• Colorectal cancer: HR 0.80 (95% CI 0.72-0.89)

Though to a lesser degree, some benefit was observed for relapsing and transient quitters, "reaffirming a linear decreasing trend in the order of continuous smokers, relapsed quitters, transient quitters, complete quitters, and never smokers," the researchers wrote in .

Notably, complete quitters had a cancer risk that was slightly higher than that of continuous smokers for the first 10 years after quitting (HR 1.12, 95% CI 1.08-1.16), but the risk decreased sharply when individuals reached 15 years of cessation or more (HR 0.41, 95% CI 0.38-0.44).

"The observed increase in the cancer risk following smoking cessation may be attributed to the inclusion of individuals who had already accumulated substantial damage caused by smoking, known as sick quitters," Oh's group explained. "This trend aligns with the well-documented phenomenon of escalated medical use and associated expenses among those who have just quit."

The authors reported that regardless of when a person quit smoking within their lifetime, their cancer risk was still significantly reduced. However, when smokers quit before the age of 50, their risk was reduced to a greater degree (HR 0.43, 95% CI 0.35-0.53) than if they quit after reaching age 50 (HR 0.61, 95% CI 0.56-0.66).

E. Neil Schachter, MD, of Mount Sinai Health System in New York City, suggested to 木瓜直播 that the slow development of cancer itself, which requires multiple genetic mutations in the cells affected, may play a role in the long-term divergence of incident cancer rates.

"Somebody who quits at an earlier age probably has -- number one -- less of these damaged DNA segments and also is probably a little bit better equipped to repair them," he commented.

Schachter stressed that among those who have quit, utilizing diagnostic tools like CT scans alongside preventative strategies is key to hopefully catching cancer in its earlier stages.

"Even in that high-risk period after the first 10 years when there continues to be an increase in the number of cancers, particularly lung cancer, there is a good chance that if they take advantage of these preventive programs, that they will come out with a good result," he said.

For the study, Oh and colleagues relied on data from the National Health Insurance Service in South Korea. Individuals included were those who underwent health screening during the baseline period (years 2002 and 2003) and were followed out to 2017.

Patients who had died or were diagnosed with cancer prior to 2006 were not included in the analysis, as were those missing certain informational data such as smoking duration, BMI, and income level.

Ultimately, 2,974,820 participants were included in the analysis. Approximately 42% were women, and the average age was 49 years for women and 43 for men.

Health exams were conducted in 2-year examination cycles. Based on the smoking status listed in these reports, patients were categorized as complete quitters, transient quitters (alternating between current and former smoking in the following examination cycles), relapsed quitters, continuous smokers, and never smokers.

Over the mean 13.4 years of follow-up, 196,829 cancer diagnoses were confirmed.

Lung cancer was the first type of cancer to be impacted by smoking cessation, decreasing, on average, 3 years earlier than the other types of cancer analyzed, the investigators found.

Researchers excluded people who were past smokers at baseline and only counted years of smoking cessation for those who quit smoking during the study period.

"Considering that older individuals who quit smoking are more likely to have a longer duration of smoking cessation, it is important to address this confounding effect, particularly in studies involving participants spanning various age ranges," Oh's group wrote.

Nevertheless, the researchers did explain that selection bias may have been introduced to the study, as analysis required "consecutive examinations of biennial health screens" as a way to determine smoking status on a consistent basis.

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