LOS ANGELES — A new study of prostate cancer suggests that a tumor's aggressiveness is inherently fixed at the time of its appearance, although diet, lifestyle and environmental factors may trigger progression of the disease in low-level cases.
The findings, which were published Wednesday in the journal Cancer Research, add to mounting evidence that many small, slow-growing prostate tumors can be left in the body and carefully monitored instead of being treated with surgery, radiation, hormone therapy or drugs.
Doctors call this approach “active surveillance,” and it's increasingly seen as a way to reduce men's risk of such side effects such as incontinence and erectile dysfunction after treating tumors that would not have killed them.
In related news, long-term results from a major federal study should ease worries about the safety of a hormone-blocking drug that can lower a man's chances of developing prostate cancer.
The drug reduced prostate cancer risk by 30 percent without raising the risk of dying of an aggressive form of the disease, as earlier results hinted it might.
The new work could prompt a fresh look at using the drug for cancer prevention. Experts say it could prevent tens of thousands of cases a year, saving many men from treatments with seriously unpleasant side effects.
The drug is sold as Proscar and in generic form as finasteride to treat urinary problems resulting from an enlarged prostate. It's also sold in a lower dose as Propecia to treat hair loss.
A decade ago, the drug was found to cut the risk of prostate cancer. But there was a small rise in aggressive tumors among its users. Some researchers said that by shrinking the prostate, the drug was just making these tumors easier to find in a biopsy sample — not causing them.
But the concern led the Food and Drug Administration to turn it down for cancer prevention and add warnings to its label.
Now, with 18 years of follow-up from that earlier study, researchers report that men on the drug were no more likely to die than those not taking it. The drug can cause hot flashes, fatigue, weakness, low sex drive and trouble having sex.
The National Cancer Institute estimates that 238,590 men will be newly diagnosed with prostate cancer this year, though the tumors are generally slow-growing and most patients will die of something else.
Scientists in the Cancer Research study set out to determine whether prostate tumors begin as indolent growths and become more dangerous over time, or whether their level of aggressiveness remains constant.
The report's authors examined 1,200 cases of men who had the prostate gland removed from 1982 to 2004 because of cancer.
The sample consisted of men diagnosed before and after introduction of the prostate-specific antigen test in the early 1990s, which became a popular tool to diagnose prostate cancer in men who hadn't developed symptoms.
The researchers focused on two measures that are often used to predict a tumor's behavior.
The first measure, stage, describes the extent to which a cancer has spread. The second measure, Gleason score, describes just how normal or abnormal the cells are in the diseased tissue.
As expected, the incidence of advanced-stage cancers plummeted after PSA screening was introduced, because more cases were caught early. Late-stage cancers made up 20 percent of the cases diagnosed from 1982 to 1993 but constituted only 3 percent of the cases diagnosed from 2000 to 2004.
In contrast, the number of high Gleason grade cancers held relatively steady: They made up 25 percent of the sample from 1982 to 1993 and dropped to 18 percent from 2000 to 2004. That difference was not deemed statistically significant.
The researchers determined that the cancer's aggressiveness must remain fixed; otherwise, high Gleason scores would have dropped more sharply, in line with the advanced-stage cancers.
Study leader Kathryn Penney, an epidemiologist at Boston's Brigham and Women's Hospital and the Harvard School of Public Health, said the results support use of active surveillance for most prostate cancer patients.
“This isn't a reason in and of itself to take active surveillance,” she said. “But if a patient's physician recommends active surveillance, and the patient agrees, this finding can make a man feel more comfortable about making that choice.”
Penney acknowledged that there were still men with high grades of the disease who survived and men with low grades who died of cancer.
“We think that while Gleason itself might be a fixed characteristic, there are likely other factors that are playing a role,” such as diet and lifestyle factors like smoking, she said.
Dr. Robert Reiter, director of the prostate cancer program at the University of California, Los Angeles, said the study was important because it addressed the fundamental question of whether cancers become more aggressive over time.
But the data showed that not all cancers were fixed, and that some did change. The challenge for clinicians, Reiter said, was to “identify ones that have the potential to morph over time versus those that do not.”
This article includes material from the Associated Press.