cancer prevention

Cancer prevention: On the horizon
Specialists in cancer prevention are increasingly optimistic about investigations such as the Study of Tamoxifen and Raloxifene (STAR), the Breast Cancer Prevention Trial (BCPT), and the Prostate Cancer Prevention Trial (PCPT). There seem to be many reasons for optimism.
Prostate Cancer Prevention Trial
The PCPT was closed a year ahead of schedule because of its findings showing that men taking finasteride experienced a clear benefit. In brief, investigators randomized 18,882 men aged 55 years and older with normal digital rectal examination findings and prostate-specific antigen (PSA) levels of 3 ng/mL or less to receive 5 mg/d of finasteride or placebo. Follow-up continued for 7 years. Prostate cancer was detected 18.4% of the finasteride group and 24.4% of the placebo group. However, higher-grade tumors (Gleason grade 7, 8, 9, or 10) were more common (37%) in the finasteride than the placebo group (22.2%). Urinary side effects were more common in the placebo group, while sexual side effects caused more difficulties among men in the finasteride group. The investigators concluded that finasteride prevents or delays the appearance of prostate cancer. Many experts are confident that finasteride is a powerful tool against prostate cancer. The Gleason score findings are a cause for further investigation, but because this scoring system was not developed for use in men taking finasteride or other medications, the findings may be artifactual.1 Finasteride causes decreases in prostate volume, which increases the ratio of tumor volume to prostate volume. A reduction in prostate volume, therefore, might increase the risk of finding a high-grade tumor.
The Breast Cancer Prevention Trial
Cancer experts describe the BCPT as "amazing" and "a breakthrough." A test of whether tamoxifen could prevent breast cancer in high-risk women involved more than 13,000 pre- and postmenopausal women at 300 centers in North America. Compared to women who were randomized to receive placebo, women who received tamoxifen had a 49% reduction in breast cancer diagnoses.2
The Study of Tamoxifen and Raloxifene
STAR has enrolled 19,000 postmenopausal women who are at high risk of breast cancer. The efficacy of tamoxifen will be compared to that of raloxifene in preventing breast cancer. Results are expected in mid-2006. The better drug in this trial will eventually compared to an aromatase inhibitor in another breast cancer prevention trial. A related trial, the Capital Area SERM Study, is assessing the efficacy and safety of raloxifene in high-risk premenopausal women.
Selenium and Vitamin E Cancer Prevention Trial
Based on evidence that selenium and vitamin E may significantly lower the risk of prostate cancer, the SELECT trial has enrolled more than 35,000 healthy men who have been randomized to one of the following regimens:
Selenium and vitamin E
Selenium and a placebo
Vitamin E and a placebo
Two placebos
Follow-up is expected to continue for 7 to 12 years. The SELECT trial is notable because 15% of participants are African American. This is a larger percentage than has been enrolled in any other cancer prevention trial.
COX-2 inhibitors, NSAIDS, and vitamin E
Trials of the COX-2 inhibitor celecoxib in the prevention of lung cancer have been resumed after a hiatus caused by the findings that these agents increase the risk of MI. A phase II trial of celecoxib in the prevention of colon cancer in patients with familial adenomatous polyposis is also in progress.
The possible cancer prevention effects of aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) have been exceedingly difficult to determine. A new study showed a modest benefit associated with aspirin in preventing prostate cancer.3 A recently published study from the Women's Health Study showed that 10 years of aspirin use had no preventive effects on total, breast, colorectal, or other site-specific cancers.4 Additional data from the Women's Health Study published at the same time showed that vitamin E had no benefit in cancer prevention or the prevention of heart disease.