Many cancer patients use psychological therapies because they expect them to cure their cancer or to improve their recovery. Despite these high expectations, both patients and oncologists report being moderately to very satisfied with the results of psychological therapies. Previous reviews of the literature have concluded that psychological therapies may help cancer patients in various ways, ranging from reducing the side effects of cancer treatments to improving patients' immune function and longevity. However, because those reviews lacked methodologic rigor, we critically and systematically reviewed all identifiable publications about psychological therapies used by cancer patients to provide an objective and scientific evaluation of nontraditional therapies. We identified 627 relevant papers that reported on 329 intervention trials by searching MEDLINE, Healthplan, Psychlit, and Allied and Complementary Medicine databases and in the bibliographies of the papers identified. Despite increased use of randomized, controlled trial designs over time, the methodologic quality of the intervention trials, on 10 internal validity indicators, was generally suboptimal, with only one trial achieving a quality rating of "good" for its methodology. Using effectiveness results from 34 trials with psychosocial outcomes, 28 trials with side effect outcomes, 10 trials with conditioned side-effect outcomes, and 10 trials with survival or immune outcomes, we make only tentative recommendations about the effectiveness of psychological therapies for improving cancer patients' outcomes. Nevertheless, by exploring the relative effectiveness of the different intervention strategies for each outcome and follow-up period, we suggest the specific therapies that should be considered for further investigation. In addition, we suggest how future trials can maximize their internal validity by describing the minimal reporting standards that should be required in this field. [ABSTRACT FROM AUTHOR]