Guest Post by William G. Nelson, MD, PhD
Editor-in-Chief, Cancer Today
The lifetime risk of a prostate cancer diagnosis for U.S. men is one in seven, with most prostate cancers discovered between ages 65 and 74. However, autopsy studies conducted by medical examiners of men not known to have prostate cancer suggest that the disease arises earlier and more commonly than these statistics suggest. In one study, pathologists looked through every nook and cranny of prostates recovered from autopsies for evidence of cancer. The findings were striking: Small prostate cancers were seen in as many as 29 percent of men between ages 30 and 40 and 64 percent between ages 60 and 70. Though only 1 in 38 men die of prostate cancer, more than two-thirds of men over age 70 carry cancer in their prostates, meaning many more men die with prostate cancer than of prostate cancer.
How can such cancers persist for decades and never cause symptoms or threaten life? Pathologists grade the potential aggressiveness of prostate cancer using the Gleason scale, which allows them to distinguish low-grade prostate cancers that grow slowly and rarely pose a health threat from high-grade prostate cancers that grow more rapidly, disseminate throughout the body and can lead to premature death. The realization that low-grade prostate cancer acts so indolently has led some to argue that the greatest hazard of this condition may be complications from surgery, radiation therapy and hormonal treatments, therapies that can be lifesaving for higher-grade disease. The mystery of why low-grade and high-grade prostate cancers act so differently has not yet been solved.
Screening and early detection of prostate cancer using blood tests for prostate specific antigen (PSA) has been widespread in the United States since the early 1990s. These tests are responsible in part for the nearly 30 percent decline in prostate cancer deaths since then. Men discovered to have prostate cancer through biopsies triggered by an abnormal PSA test tend to have small tumors that are more readily treated and cured by surgery and radiation therapy. So for men with high-grade prostate cancers, treatment resulting from PSA screening offers significant benefits. However, treatment value is less clear for men diagnosed with low-grade prostate cancers. A worry that low-grade prostate cancers may be overtreated once they are discovered by PSA testing has led to controversy over the value of prostate cancer screening. The U.S. Preventive Services Task Force (USPSTF) now formally recommends against prostate cancer screening.
One answer to the conundrum of PSA screening and overtreatment may be greater use of active surveillance for small, low-grade prostate cancers diagnosed as a result of screening. The notion is that a man found to have only low-grade prostate cancer on a biopsy might be able to avoid treatment. Active surveillance mandates vigilant follow-up and requires frequent PSA testing and repeat biopsies. This helps ensure that high-grade prostate cancer, if missed by an earlier biopsy or if it appears in the future, can be discovered and treated. Active surveillance appears to be a safe strategy, as less than 1 percent of men followed this way die of prostate cancer within 15 years.
William G. Nelson, MD, PhD, is the editor-in-chief of Cancer Today, the quarterly magazine for cancer patients, survivors, and caregivers published by the American Association for Cancer Research. Dr. Nelson is the Marion I. Knott professor of oncology and director of the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins in Baltimore. You can read his complete column in the winter 2015/2016 issue of Cancer Today.
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