Association of Age at Smoking Initiation and Cessation with Risk of Cancer Mortality

SUMMARY: According to the American Cancer Society, tobacco use is responsible for about 1 in 5 deaths in the United States and is the leading preventable cause of death in the US. Smoking (cigarettes, cigars, and pipes) is responsible for about 20% of all cancers and about 30% of all cancer deaths in the US. Approximately 80% of lung cancers, as well as about 80% of all lung cancer deaths, are due to smoking, and lung cancer is the leading cause of cancer death in both men and women. Smoking also increases the risk for cancers of the Oral cavity, Oropharynx, Larynx, Esophagus, Stomach, Liver, Pancreas, Colon/Rectum, Kidney, Bladder, Cervix, as well as Acute Myeloid Leukemia.

Previous published studies have shown that individuals who start smoking at a younger age have greater mortality risk than those who start smoking later in life, and quitting to smoke especially at younger ages substantially reduces that mortality risk. However, the relevance of age at smoking initiation and cessation to cancer mortality, in contemporary US populations, particularly across the life course, is not clear.

The authors in this prospective cohort study investigated the association between age at smoking initiation and cessation, and cancer mortality, at ages 25 to 79 years. Data for this study was used from a cohort of 410,231 participants in the US National Health Interview Survey from 1997 to 2014, linked to the National Death Index, and follow up was continued through December 31, 2015. The mean patient age was 48 years and 56% were female. Self-reported current daily smokers were categorized by age at smoking initiation (less than 10 yrs, 10-14 yrs, 15-17 yrs, 18-20 yrs, and 21 or more years). Ex-smokers were categorized by age at quitting (15-34 yrs, 35-44 yrs, 45-54 yrs, or 55-64 years). Current nondaily smokers (4% of cohort) and ex-smokers who quit at ages younger than 15 years or 65 years and older (1% of cohort) were excluded from the analysis. Cancer mortality rate ratios were adjusted for age at risk, sex, race and ethnicity, education, region and alcohol consumption.

There were 10,014 cancer deaths at ages 25 to 79 years during 3.7 million person-years of follow-up (mean=10 plus or minus 5 years). Compared with never smokers, the overall cancer mortality rate ratio associated with current smoking was 3.00, suggesting that current smoking was associated with three times the cancer mortality rate of never smoking.

For individuals who started smoking at age younger than 10 yrs, the cancer mortality rate ratio was 4.01, 3.57 for those ages 10-14 yrs, 3.15 for those ages 15-17 yrs, 2.86 for those ages 18-20 yrs and 2.44 for those ages 21 yrs and older. The researchers pointed out that if these excesses were interpreted as largely causal, smoking would account for 75% of cancer deaths among those starting before age 10 yrs and 59% among those starting at age 21 yrs and older. Those who quit smoking at ages 15-34 yrs, 35-44 yrs, 45-54 yrs, and 55-64 yrs avoided an estimated 100%, 89%, 78%, and 56% of the excess cancer mortality risk associated with continued smoking, respectively.

The authors concluded that in this contemporary US population, current smoking was associated with 3 times the cancer mortality rate of never smoking, and the researchers added that the findings from this study underscore that starting to smoke at any age is extremely hazardous. However, smokers who quit especially at younger ages can avoid most of the cancer mortality risk associated with continued smoking.

Association of Smoking Initiation and Cessation Across the Life Course and Cancer Mortality: Prospective Study of 410 000 US Adults. Thomson B, Emberson J, Lacey B, et al. JAMA Oncol. Published online October 21, 2021. doi:10.1001/jamaoncol.2021.4949