The medication finasteride, which after the seven-year Prostate Cancer Prevention Trial (PCPT) was associated with a 24.8 percent reduction of prostate cancer risk among men who took it, has a new feather in its cap – it beefs up the diagnostic power of the prostate-specific antigen (PSA) test.
A new analysis of PCPT data, published Aug. 16 in the Journal of the National Cancer Institute, suggests that finasteride not only enhanced the PSA test’s detection of prostate cancer versus no cancer, but it also improved the test’s ability to signal the more serious, high-grade cancers that, left untreated, can lead to end-stage illness and death.
“When you have a test for cancer screening, it’s very rare that you can make that test better,” said lead author Ian M. Thompson Jr., M.D., professor and chair of the department of urology at The University of Texas Health Science Center at San Antonio and the Glenda and Gary Woods Distinguished Chair in Genitourinary Oncology at the Cancer Therapy and Research Center. “Finasteride is associated with a significant improvement in the PSA test’s performance. It has multiple areas of impact in the detection and treatment of prostate cancer.”
Dr. Thompson was principal investigator of the original PCPT study that was conducted at 219 institutions and was coordinated by the Southwest Oncology Group, one of the largest cancer clinical trials cooperative groups in the nation.
Although men who were prescribed 5 milligrams of finasteride daily during the PCPT were less likely to develop prostate cancer, they were more likely to develop high-grade disease, compared to men in the control group. The second result dampened public interest in the drug, Dr. Thompson said.
The new analysis shows that the elevated risk of serious disease in the finasteride group “was due, at least in part, to improved detection (i.e., increased sensitivity of PSA) rather than solely to true induction of high-grade disease by finasteride,” the authors wrote. The drug’s positive effect on PSA performance may also lead to detection of cancers that truly need urgent attention, Dr. Thompson said.
For example, finasteride reduces the symptoms of benign prostatic hyperplasia, a prostate enlargement. “Finasteride treatment of men with elevated PSA levels would cause the greatest fall in PSA level in men with benign conditions such as benign prostatic hyperplasia, whereas men with persistently elevated PSA levels would have a higher probability of cancer,” the authors wrote.
The authors went so far as to state that it is likely the 24.8 percent reduction in prostate cancer risk with finasteride during the PCPT was “an underestimate.”
National Cancer Institute grants funded the study, which has co-authors from the Southwest Oncology Group, the Fred Hutchinson Cancer Research Center in Seattle, The University of Texas M. D. Anderson Cancer Center, the National Cancer Institute, and the University of Colorado at Denver and Health Sciences Center. Co-authors are Chen Chi, Donna Pauler Ankerst, Phyllis J. Goodman, Catherine M. Tangen, Scott M. Lippman, M. Scott Lucia, Howard L. Parnes and Charles A. Coltman Jr.
The PCPT was designed to test whether finasteride would prevent prostate cancer in men ages 55 and older. The study was closed in June 2003 – 15 months prior to the expected final date of follow-up – because the study objective had been reached. The results of the study, “The Influence of Finasteride on the Development of Prostate Cancer,” were published in the New England Journal of Medicine on July 17, 2003.
Dr. Thompson, one of the country’s most eminently recognized urologists, holds the Henry B. and Edna Smith Dielmann Memorial Chair at the Health Science Center. He is a member of the National Cancer Institute Early Detection Research Network (EDRN). He soon will open a multidisciplinary genitourinary clinic at the Cancer Therapy and Research Center.