Low-income men treated for prostate cancer are likelier to have a more aggressive disease at diagnosis compared with their better-off counterparts, a study at one U.S. public hospital suggests.

Researchers found that compared with prostate cancer patients seen at U.S. academic medical centers and private practices, an elevated rate of higher risk prostate cancer was seen among men treated at San Francisco General Hospital - a publicly funded “safety net” hospital that primarily serves the low-income and uninsured.

The greater proportion of high-risk cancers could not be explained away solely by later diagnoses due to a lack of screening. The researchers speculate several factors may be at work.

“High-risk” prostate cancer refers to tumors that have an increased likelihood of spreading and becoming life threatening - because they are relatively extensive or have abnormalities that make them particularly aggressive, for instance.

Most prostate tumors are slow-growing, and may never advance far enough to shorten a man’s life. This means that many men diagnosed with the disease can choose to forgo treatment in favor of periodic tests to monitor the cancer’s progression. But prompt treatment, with surgery, radiation or other therapies may be recommended for men with higher risk prostate cancer.

MORE DANGEROUS TUMORS

In the current study, researchers found that of 377 men diagnosed with prostate cancer at the San Francisco public hospital between 1998 and 2008, only 29 percent had low-risk disease - based on the stage of the tumor, blood levels of prostate-specific antigen (PSA) and Gleason score, a measure of the tumor’s aggressiveness.

In contrast, low-risk cancer was found in about 39 percent of men included in two large prostate cancer databases - one of patients treated at 31 U.S. academic medical centers and community-based practices since 1995, and one of men treated at the University of California, San Francisco (UCSF) between 1997 and 2007.

The rest of the men treated at San Francisco General Hospital - 61 percent - had either high- or intermediate-risk prostate cancer, or had tumors that had already spread beyond the prostate.

Of men at the public hospital, 12 percent had cancer that had spread to the seminal vesicles outside the prostate gland, nearby lymph nodes or beyond.

That compared with roughly 4 percent in the national database and just under 7 percent in the UCSF registry, the researchers report in the Journal of Urology.

“What’s driving this? Right now, it’s up in the air,” said senior researcher Dr. Matthew R. Cooperberg, an assistant professor of urology at UCSF, in an interview.

The difference does not appear to be explained by disparities in access to medical care, Cooperberg told Reuters Health. He noted that many men at the public hospital had undergone routine prostate cancer screening.

Black men are at higher risk of prostate cancer than other racial groups, and the San Francisco General Hospital group had a larger percentage of African Americans than the two databases used for comparison.

However, Cooperberg said, racial differences do not appear to fully account for the greater burden of intermediate- to high-risk cancer among lower income men.

He and his colleagues speculate that there could be a range of factors involved, including some as-yet unidentified genetic factors that may affect prostate cancer progression in different ethnic groups. They say there might also be a role for differences in obesity rates, diet or environmental exposures - although it is not clear whether obesity or any dietary or environmental factor directly affects prostate tumors’ aggressiveness.

Cooperberg’s team also speculates that the chronic stress of living in poverty could be a factor. He pointed to animal research supporting the theory that chronic stress, which can dampen immune system activity, might affect the progression of cancer. But again, the role of stress in prostate cancer progression, if any, is not known.

Cooperberg said that more research is needed both to confirm the current findings in other public hospitals, and to try to uncover the underlying reasons.

He said his team’s findings could also have implications for prostate cancer screening.

REDIRECT SCREENING EFFORT

Routine screening with digital rectal exams and PSA testing is controversial. Because prostate tumors are often slow growing, screening that detects small, lower risk tumors may result in many men being treated for cancers that would never have caused them problems. So those treatments - with their risks of side effects like erectile dysfunction and urinary incontinence - can do more harm than good for some men.

A U.S. study last year estimated that routine prostate screening has resulted in more than 1 million U.S. men being diagnosed with tumors that would never have caused them any serious problems. Another study published earlier this month in the medical journal BMJ concluded there is no evidence that all of this screening has cut death rates from the disease.

Cooperberg agreed, “Overtreatment of prostate cancer is a problem.” But he added that PSA screening may be relatively more beneficial for lower income men, who appear to have a greater chance of high-risk prostate cancer than their better-off counterparts.

More research attention should go toward examining the effects of targeted screening in public hospitals, rather than at academic medical centers, he argued.

Right now, medical groups differ in their recommendations for prostate cancer screening. According to the American Cancer Society, men age 50 and up should discuss the pros and cons of screening with their doctors to come to an informed decision.

The group also says that, because of their higher than average risk, African-American men should have that discussion starting at age 45. The same advice stands for men who have a father, brother or son who was diagnosed with prostate cancer before the age of 65.

SOURCE:  Journal of Urology, online September 17, 2010.