Cigarette tar yields in relation to mortality from lung cancer in the cancer prevention study II prospective cohort, 1982-8

Our plain-English summary of Cigarette tar yields in relation to mortality from lung cancer in the cancer prevention study II prospective cohort, 1982-8, by J.E. Harris, M.J. Thun, A.M. Mondul, et al (BMJ, 2004).

The study

• Authors: J.E. Harris, M.J. Thun, A.M. Mondul, E.E. Calle
• Journal: BMJ
• Published: 2004;328(7431):72
• Cited by: 101 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: To assess the risk of lung cancer in smokers of medium tar filter cigarettes compared with smokers of low tar and very low tar filter cigarettes.

Design: Analysis of the association between the tar rating of the brand of cigarette smoked in 1982 and mortality from lung cancer over the next six years. Multivariate proportional hazards analyses used to assess hazard ratios, with adjustment for age at enrollment, race, educational level, marital status, blue collar employment, occupational exposure to asbestos, intake of vegetables, citrus fruits, and vitamins, and, in analyses of current and former smokers, for age when they started to smoke and number of cigarettes smoked per day.

Setting: Cancer prevention study II (CPS-II).

Participants: 364 239 men and 576 535 women, aged > or = 30 years, who had either never smoked, were former smokers, or were currently smoking a specific brand of cigarette when they were enrolled in the cancer prevention study.

Main Outcome Measure: Death from primary cancer of the lung among participants who had never smoked, former smokers, smokers of very low tar (< or = 7 mg tar/cigarette) filter, low tar (8-14 mg) filter, high tar (> or = 22 mg) non-filter brands and medium tar conventional filter brands (15-21 mg).

Results: Irrespective of the tar level of their current brand, all current smokers had a far greater risk of lung cancer than people who had stopped smoking or had never smoked. Compared with smokers of medium tar (15-21 mg) filter cigarettes, risk was higher among men and women who smoked high tar (> or = 22 mg) non-filter brands (hazard ratio 1.44, 95% confidence interval 1.20 to 1.73, and 1.64, 1.26 to 2.15, respectively). There was no difference in risk among men who smoked brands rated as very low tar (1.17, 0.95 to 1.45) or low tar (1.02, 0.90 to 1.16) compared with those who smoked medium tar brands. The same was seen for women (0.98, 0.80 to 1.21, and 0.95, 0.82 to 1.11, respectively).

Conclusion: The increase in lung cancer risk is similar in people who smoke medium tar cigarettes (15-21 mg), low tar cigarettes (8-14 mg), or very low tar cigarettes (< or = 7 mg). Men and women who smoke non-filtered cigarettes with tar ratings > or = 22 mg have an even higher risk of lung cancer.

In plain English

Using the American Cancer Society's Cancer Prevention Study II, a US nationwide prospective cohort, the authors followed 364,239 men and 576,535 women aged 30 or older from 1982 to 1988. They compared the tar rating of the cigarette brand each current smoker reported in 1982 with later death from lung cancer. Asbestos was not the subject of the study. Having worked 10 years or more in a job with high asbestos exposure was one of several factors the analysis adjusted for. Over six years, 2622 men and 1406 women died of lung cancer. Compared with smokers of medium tar (15-21 mg) filter brands, risk was higher for smokers of high tar (22 mg or more) non-filter brands: hazard ratio 1.44 (95% confidence interval 1.20 to 1.73) in men and 1.64 (1.26 to 2.15) in women. The authors found no difference in risk for smokers of low tar (8-14 mg) or very low tar (7 mg or less) brands compared with medium tar smokers. The authors concluded that lung cancer risk was similar across medium, low and very low tar cigarettes.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Prospective cohort study: analysis of the Cancer Prevention Study II (CPS-II), with six years of mortality follow-up (1982-8) and Cox proportional hazards analyses, done separately for men and women
• Who was studied: 364,239 men and 576,535 women aged 30 or older in the American Cancer Society's US nationwide CPS-II cohort. They were never smokers, former smokers, or current smokers of a specific brand at enrolment in 1982, and were followed to 1988. People with a history of cancer other than non-melanoma skin cancer, men who ever used pipes, cigars or chewing tobacco, and people whose smoking status was unknown were excluded.
• Exposure: The tar rating of the cigarette brand smoked in 1982, in four groups: very low (7 mg or less), low (8-14 mg), medium (15-21 mg, the comparison group) and high (22 mg or more, non-filter). Asbestos was not studied as an exposure. Employment for 10 years or more in an occupation with high asbestos exposure (such as pipe fitters and shipyard workers) was used only as an adjustment factor.
• Main results:
  • During the six-year follow-up, 2622 men and 1406 women in the cohort died from cancer of the trachea, bronchus, or lung.
  • Compared with current smokers of medium tar (15-21 mg) filter cigarettes, current smokers of high tar (22 mg or more) non-filter brands had higher risk. The hazard ratio was 1.44 (95% CI 1.20 to 1.73) in men and 1.64 (1.26 to 2.15) in women.
  • Compared with medium tar smokers, men who smoked very low tar brands had a hazard ratio of 1.17 (0.95 to 1.45) and men who smoked low tar brands had 1.02 (0.90 to 1.16). The authors reported no difference in risk.
  • Women who smoked very low tar brands had a hazard ratio of 0.98 (0.80 to 1.21) and women who smoked low tar brands had 0.95 (0.82 to 1.11), compared with medium tar smokers.
  • The test of whether risks differed across the very low, low and medium tar groups gave p = 0.27 for men and p = 0.80 for women. The authors described these risks as indistinguishable.
  • Compared with current medium tar smokers, men who had quit smoking had adjusted hazard ratios of 0.06 (0.04 to 0.09) if they quit by about age 35, 0.23 (0.20 to 0.27) if they quit at 35-54, and 0.63 (0.55 to 0.71) if they quit at 55 or older.
  • For women who had quit smoking, the corresponding adjusted hazard ratios were 0.09 (0.05 to 0.14), 0.26 (0.21 to 0.32) and 0.47 (0.38 to 0.59).
  • In both men and women, the findings were essentially unchanged in sensitivity analyses. These excluded people with emphysema and other smoking-related diseases, restricted the analysis to people who had smoked their current brand for at least 5 or 10 years, or slightly changed the tar category boundaries.
• The authors' conclusion: The authors concluded that the increase in lung cancer risk is similar in people who smoke medium tar (15-21 mg), low tar (8-14 mg), or very low tar (7 mg or less) cigarettes. They also concluded that men and women who smoke non-filtered cigarettes rated 22 mg or more have an even higher risk.
• Limitations the authors state:
  • Smoking habits of all participants were recorded only at enrolment in 1982.
  • The American Cancer Society did not collect information on changes in smoking behaviour during follow-up of the whole cohort. For this reason, follow-up was restricted to six years.
  • Most current smokers could not have smoked low or very low tar brands throughout their lives, so the effect of using only these cigarettes from adolescence onward could not be evaluated.
  • The higher risk found in smokers of high tar non-filter cigarettes may reflect unmeasured differences between non-filter and filter smokers.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Hazard Ratio, Occupational Exposure, confidence interval.

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