Study designs of evaluations included in the review
Phase III randomised controlled trials (RCTs) were eligible for inclusion. Most of the included primary prevention studies were blinded.
Specific interventions included in the review
Studies of chemopreventive agents targeting primary, secondary and tertiary prevention were eligible for inclusion. Primary prevention focuses on treating those people with known risk factors; secondary prevention is used for those people with identifiable precursor lesions; and tertiary prevention is used to treat people who had received treatment for a prior cancer. The included studies used alpha-tocopherol, beta-carotene, retinol, vitamin E and aspirin for primary prevention; beta-carotene, N-acetylcysteine, isotretinoin, or retinol or retinyl palmitate for tertiary prevention.
Participants included in the review
The authors did not specify any inclusion criteria relating to the participants. The primary prevention studies included smokers and non-smokers; the tertiary prevention studies included patients with head and neck and/or lung cancer.
Outcomes assessed in the review
The outcome eligible for inclusion was lung cancer incidence. In the tertiary prevention studies this was defined as a second primary tumour.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.