This year, more than 238,000 American men will be diagnosed with prostate cancer. In most cases, cancer consists of small knots of abnormal cells growing slowly in the walnut-sized prostate gland. In many men, the cancer cells grow so slowly that they never break free of the gland, spread to distant sites, and pose a serious risk to health and longevity.
Evidence is growing that early treatment with surgery or radiation prevents relatively few men from ultimately dying from prostate cancer while leaving many with urinary or erectile problems and other side effects. As a result, more men may be willing to consider a strategy called active surveillance, in which doctors monitor low-risk cancers closely and consider treatment only when the disease appears to make threatening moves towards growing and spreading.
A study by Harvard researchers found that the aggressiveness of prostate cancer at diagnosis appears to remain stable over time for most men. If that is true, then prompt treatment can be reserved for the cancers most likely to pose a threat, whereas men can reasonably choose to watch and wait in other cases.
The study looked for changes in cancer aggressiveness in men diagnosed with prostate cancer from 1982 to 2004. All of then men had their prostates removed after diagnosis, and biopsy samples were taken from the glands. The Harvard team re-examined the samples and graded them using a tool called the Gleason score, which assigns a number from 2 to 10 based on how abnormal the cells look under a microscope. High scoring or “high-grade cancers” tend to be the most lethal.
Over the study period, fewer and fewer men were diagnosed with advanced, late-stage prostate cancers that had spread beyond the prostate gland. This reflected the growing use of prostate-specific antigen testing to diagnose prostate cancers earlier and earlier. In contrast, the proportion of high-grade cancers, as measured by the Gleason score, remained relatively stable rather than gradually becoming more aggressive. Previous studies have seen a similar pattern.
That means most prostate cancers that look to be slow growing at diagnosis could stay that way long enough that the men are likely to die from another cause before cancer spreads beyond the prostate. The ones that are low grade and indolent are unlikely to cause problems in a man’s lifetime.
Gleason grade is one of the best predictors of prostate cancer death. Men with a low-grade disease are much less likely to die from prostate cancer than men with high-grade cancers. You might see a progression in an individual, but we think that it is uncommon.