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Cigarette Smoking: Health Risks and How to Quit (PDQ®): Prevention - Health Professional Information [NCI] - Summary of Evidence

Note: A separate PDQ summary on Levels of Evidence for Cancer Screening and Prevention Studies is also available.

The cancer prevention summaries in PDQ refer to cancer prevention, defined as a reduction in the incidence of cancer. The PDQ includes summaries generally classified by histological type of cancer, especially when there are known risk factors for the specific types of cancer. This summary addresses a specific risk factor, tobacco use, which is associated with a large number of different cancers (and other chronic diseases) and unequivocally contains human carcinogens.[1] The focus of this summary is on clinical interventions by health professionals that decrease the use of tobacco.

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Study Design Categories, Definitions, and Levels of Evidence

Prospective, randomized, controlled trials and meta-analyses of prospective, randomized, controlled trials. The randomized, double-blinded, controlled trial is the gold standard of study design. To achieve this ranking, the study allocation must be blinded to the investigator both before and after the randomization and the assignment to intervention group. This design provides protection from allocation bias by the investigator and from bias in the assessment of outcomes by both the...

Read the Study Design Categories, Definitions, and Levels of Evidence article > >

Effects of Smoking Cessation

Based on solid evidence, cigarette smoking causes cancers of the lung, oral cavity and pharynx, larynx, esophagus, bladder, kidney, pancreas, stomach, uterine cervix, and acute myeloid leukemia.[2] Smoking avoidance and smoking cessation result in decreased incidence and mortality from cancer.

Description of the Evidence

  • Study Design: Evidence obtained from a randomized controlled trial.
  • Internal Validity: Good.
  • Consistency: Good.
  • Magnitude of Effects on Health Outcomes: The relative risk (RR) of several cancers is much greater in cigarette smokers compared with nonsmokers (depending on the anatomical site of the cancer and the intensity and duration of smoking, the RR can range from twofold to tenfold or greater in smoking populations). A reduction of 15% is seen in the RR of all-cause mortality in heavy smokers subjected to intensive clinical cessation interventions.
  • External Validity: Good.

Counseling and Smoking Cessation

Based on solid evidence, counseling by a health professional improves smoking cessation rates.

Description of the Evidence

  • Study Design: Evidence obtained from randomized controlled trials.
  • Internal Validity: Good.
  • Consistency: Good.
  • Magnitude of Effects on Health Outcomes: Counseling improves cessation rates (odds ratio [OR], 1.56; 95% confidence interval [CI], 1.32–1.84).[3,4]
  • External Validity: Good.

Physician Advice and Smoking Cessation

Based on solid evidence, simple advice from a physician to stop smoking improves smoking cessation rates.

  • Study Design: Evidence obtained from randomized controlled trials.
  • Internal Validity: Good.
  • Consistency: Good.
  • Magnitude of Effects on Health Outcomes: Physician advice improves cessation rates (relative risk [RR], 1.66; 95% CI, 1.42–1.94).[3]
  • External Validity: Good.
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