SEATTLE—Trials in the past decade offer the first evidence that some of the most prevalent cancers in the population are preventable, and a host of ongoing trials are testing new prevention strategies, Peter Greenwald, MD, DrPH, director of the National Cancer Institute's Division of Cancer Prevention, said at the 50th Annual Meeting of the Southwest Oncology Group (SWOG). However, he noted, critical challenges in the future will include putting the knowledge gained into practice and ensuring an adequate supply of health care professionals to implement prevention efforts.
Dr. Greenwald noted that this year marks the 23rd anniversary of the Community Clinical Oncology Program (CCOP), the main mechanism by which NCI provides funding for clinical cancer prevention trials. The program currently has 3,325 participating physicians, 390 participating hospitals, and 56 ongoing cancer prevention and control trials.
Prostate Cancer Prevention
The Prostate Cancer Prevention Trial, conducted among men who had a PSA level of 3 ng/mL or lower, found that relative to placebo, finasteride(Drug information on finasteride) was associated with a roughly 25% reduction in the incidence of prostate cancer of any grade, but also with a higher incidence of cancers of Gleason grades 7-10, Dr. Greenwald said. Subsequent investigation suggested that the latter finding was likely due to a detection bias related to finasteride- induced shrinkage of the prostate and, therefore, a greater likelihood of hitting a high-grade area of a cancer during a biopsy. Furthermore, he noted, analyses restricted to men with tumors of Gleason grades 8-10 showed that among those treated with finasteride, the tumors were smaller and less often had aggressive features.
“Based on this SWOG-led study, we have the first definitive evidence that prostate cancer, at least in part, is preventable,” Dr. Greenwald commented. “We also have a unique tissue bank with controls that is helping in a major reevaluation of the PSA test, and providing a lead toward understanding, at a biological level, what makes these tumors aggressive.”
He noted that further data on prostate cancer prevention are awaited from the Selenium(Drug information on selenium) and Vitamin E(Drug information on vitamin e) Cancer Prevention Trial (SELECT), in which men are receiving one or both supplements, or placebos, for 7 years. “It is a wonderful trial. It is in progress. It is tremendously well run and managed,” he said.
Breast Cancer Prevention
The Breast Cancer Prevention Trial found that relative to placebo, tamoxifen(Drug information on tamoxifen) was associated with a nearly 50% reduction in the incidence of breast cancer among women at high risk, Dr. Greenwald said. Further, the Multiple Outcomes of Raloxifene(Drug information on raloxifene) Evaluation (MORE) trial found a 76% reduction in the risk of invasive breast cancers with raloxifene (Evista), compared with placebo among postmenopausal women with osteoporosis. “These two trials were the main driving factor for the decision to initiate the STAR [Study of Tamoxifen and Raloxifene] trial, the head-to-head comparison of tamoxifen and raloxifene,” he said.
In the recently reported STAR trial, among postmenopausal women, the two drugs were equally effective in preventing primary invasive breast cancer, achieving reductions of 40% to 50%, while raloxifene was less effective in preventing noninvasive breast cancers.