NEW YORK (Reuters) -- After rising sharply for three years in a row, the number of new cases of prostate cancer in the U.S. is on the decline.
From 1992 to 1993, the latest data available for analysis, prostate cancer incidence rates dropped by 16% for white men, while stabilizing at a 2% increase among African-American men. The findings are reported in the November 20 issue of the Journal of the National Cancer Institute (NCI).
"No one who has been following the data closely should be surprised by the decrease. Now we need to pursue why it's decreasing," said Dr. Ray M. Merrill, one of the authors of the report.
The decline in age-adjusted prostate cancer incidence differs sharply from the dramatic increase in incidence observed from 1989 to 1992. During that period, the incidence rate increased 61% among whites, and 65% among African Americans.
Merrill and his colleagues at the NCI explain that much of the increase in prostate cancer incidence has been attributed to the widespread use of prostate-specific antigen (PSA) for screening and detection of prostate cancer. PSA is a protein produced by the prostate gland that is often found at higher-than-normal levels in patients with cancer or other diseases of the prostate.
"It's certainly possible that when you introduce a new early screening tool such as PSA, you're going to catch many cases you wouldn't have caught until much later on," said Merrill.
By 1992, however, the trend reversed itself. Researchers analyzing data from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) cancer registry found that prostate cancer incidence rates began to fall, initially for whites in the Seattle-Puget Sound area.
"It could be that doctors in our area are becoming more discriminating about who we screen," said Dr. Paul Lange, professor and chairman of the Department of Urology at the University of Washington in Seattle. "Perhaps now that we've found all the patients that should have been picked up earlier, we're settling down to what the rate should be," said Lange.
The decline in prostate cancer incidence was seen elsewhere in the U.S. beginning in 1993, and is now evident in each of the nine geographic areas the SEER registry monitors. The rate of decline was highest in Metropolitan Detroit, Utah and Seattle; and lowest in Connecticut and Iowa.
"This suggests that there's a difference in the use of PSA screening in these areas," said Merrill, who is currently studying geographic variations in testing procedures.
Declining rates of prostate cancer incidence were observed among older age groups first, for both whites and African Americans. Declines in the incidence rate among younger age groups have only recently been identified. The finding is not unexpected, according to the study authors, as cancer screening tends to identify cases earlier, thereby increasing the rates in younger age groups while lowering the rates in older age groups.
Merrill and his colleagues suggest that additional research is needed to account for the recent drop in prostate cancer incidence rates. They speculate that the decline may reflect unresolved issues concerning the value of early detection of prostate cancer, and the morbidity and mortality associated with early treatment. These issues may have led to decreased use of PSA for screening and detection.
The increasing influence of managed care organizations may also be having an impact, says Lange, "as more and more organizations, particularly HMOs, hold the line on PSA testing until more is known."
Lange believes there is a growing number of doctors who believe that early detection of prostate cancer before symptoms are present, particularly among the oldest age groups, may worry patients unnecessarily.
"This report doesn't speak pro or con for PSA screening. What everyone wants is data on whether the mortality rate is going down, too. For now, it certainly doesn't prove that screening is right or wrong," said Lange.
Prostate cancer is the second leading cause of cancer death in men, and twice as deadly among African Americans than among whites. An estimated 317,100 new cases will be diagnosed in 1996, and an estimated 41,400 patients will die of the disease, according to the American Cancer Society.
SOURCE: Journal of the National Cancer Institute (1996;88(22):1683-1685)
