In a study reported in a research letter in JAMA Oncology, Thomson et al found that current smokers had a threefold greater risk of overall cancer mortality between the ages of 25 and 79 years vs never-smokers, with risk being modulated according to age at smoking initiation and age at cessation in those who stopped smoking.
The prospective cohort study assessed association between age at smoking initiation and cessation and mortality from any cancer from ages 25 to 79 years. Researchers used data from a cohort of 410,231 participants in the U.S. National Health Interview Survey for 1997–2014 linked to the National Death Index. Follow-up was performed through the end of December 2015.
Self-reported current daily smokers were categorized by age at smoking initiation (< 10 to ≥ 21 years), and ex-smokers were categorized by age at cessation (15–64 years). Current non–daily smokers (4% of cohort) and ex-smokers who quit at age < 15 or ≥ 65 years (1% of cohort) were excluded from the analysis. Cancer mortality rate ratios were adjusted for age at risk, sex, education, alcohol consumption, race/ethnicity, and U.S. region.
In this contemporary U.S. population, current smoking was associated with three times the cancer mortality rate of never smoking. Although delayed smoking initiation was associated with substantial reductions in cancer mortality risk, those who began smoking at ages 21 years and older nevertheless had more than twice the risk compared with never-smokers. Quitting, even at older ages, was associated with a substantial reversal of these risks.— Thomson et al
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Among the 410,231 participants (mean age = 48 ± 15 years; 56% female), 10,014 died from cancer at ages 25 to 79 years during 3.7 million person-years of follow-up (mean = 10 ± 5 years). Compared with never-smokers, the overall cancer mortality rate ratio associated with current smoking was 3.00 (95% confidence interval [CI] = 2.86–3.16).
Overall cancer mortality rate ratios according to age at smoking initiation were 4.01 (95% CI = 3.33–4.82) for < 10 years, 3.57 (95% CI = 3.29–3.87) for 10 to 14 years, 3.15 (95% CI = 2.94–3.37) for 15 to 17 years, 2.86 (95% CI = 2.65–3.08), for 18 to 20 years, and 2.44 (95% CI = 2.24–2.67) for ≥ 21 years. On the assumption that the excess cancer mortality was largely causal, smoking would account for 75% of overall cancer deaths among those starting at < 10 years and 59% among those starting at age ≥ 21 years.
Compared with never-smokers, the overall cancer rate ratios according to age at cessation were 0.95 (95% CI = 0.88–1.04) for 15 to 34 years, 1.23 (95% CI = 1.13–1.33) for 35 to 44 years, 1.45 (95% CI = 1.34–1.57) for 45 to 54 years, and 1.88 (95% CI = 1.73–2.05) for 55 to 64 years. Quitting at these age intervals would avoid an estimated 100%, 89%, 78%, and 56% of excess cancer mortality risk associated with continued smoking, respectively.
As stated by the investigators, “In this contemporary U.S. population, current smoking was associated with three times the cancer mortality rate of never smoking. Although delayed smoking initiation was associated with substantial reductions in cancer mortality risk, those who began smoking at ages 21 years and older nevertheless had more than twice the risk compared with never-smokers. Quitting, even at older ages, was associated with a substantial reversal of these risks.”
Blake Thomson, DPhil, of the Department of Surveillance and Health Equity Science, American Cancer Society, is the corresponding author for the JAMA Oncology article.
Disclosure: The study was supported by the Intramural Research Department of the American Cancer Society. For full disclosures of the study authors, visit jamanetwork.com.The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.