Metastatic prostate cancer continues to decline in incidence, but the proportion of cases being diagnosed in younger men is increasing, according to a study.

Researchers analyzed population-based cancer registry data from 24,251 cases of stage IV prostate cancer diagnosed from 1988 to 2003. They obtained data from the Surveillance, Epidemiology, and End Results (SEER) Program.

Overall, the age-adjusted incidence of stage IV prostate cancer decreased from 28.1 per 100,000 population in 1988 to 12.3 per 100,000 in 2003, an average annual decline of 6.4%, investigators reported in Urology (2009; published online ahead of print). Patients with distant metastases at diagnosis experienced an even steeper decline, from 18.4 per 100,000 in 1988 to 6.7 per 100,000 in 2003, average annual decline of 8%.

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The percentage of men aged 35-60 years diagnosed with metastatic prostate cancer, however, increased during the study period. Among men diagnosed during 1988-1992, 1%, 2.6%, and 6.8% were aged 35-50, 51-55, and 56-60 years, respectively, according to the study, which was funded by Amgen, Inc., of Thousand Oaks, Calif. These percentages increased to 4.4%, 8.5%, and 12.5%, respectively, for men diagnosed during 1998-2003.

During the study period, five-year relative survival improved 41.6% to 62.3%, especially among men diagnosed at younger ages or with moderately to well-differentiated tumors.

For men aged 35-50 years, relative five-year survival rose from 33.0% in 1988-1992 to 64.8% in 1998-2001; for men aged 51-60 years, it increased from 49.8% to 76.7%. Among those aged 61-70 years, it increased from 50.5% to 72.0%. Conversely, for those aged 71 years and older, survival was 44.1% and 41.1% in 1988-1992 and 1998-2001, respectively.

Men with distant metastases experienced only modest improvements in survival during the study period. In this group, five-year relative survival rose from 25% for those diagnosed in 1988 to 36.2% for men diagnosed in 1992, but then decreased to 27% for men diagnosed in 2001.

Five-year relative survival improved slightly only for younger patients or those with moderately to well-differentiated tumors, “suggesting that only a subset of patients with distant stage prostate cancer has benefited from more aggressive or better systemic therapies,” the investigators noted.

Furthermore, the study showed that older age (71 years or older), black race, higher tumor grade, and lack of radical prostatectomy generally conferred a poorer prognosis, “most likely reflecting differences between subgroups of patients with respect to biological factors related to survival, access to care, nature and extent of comorbiditiy, and response to available treatments.”

The proportion of stage IV tumors that were poorly differentiated at diagnosis rose significantly from 42.7% during the period 1988 to 1992 to 48.8% during 1998 to 2003, and the percentage of those of lower grades decreased.

The proportion of men who received radiation as part of first-line therapy increased slightly during the study period, primarily among men with distant metastases, but more than 75% of patients did not receive any form of radiation, the authors reported.

In addition, the researchers, led by Karynsa Cetin, MPH, of Amgen, observed a significant increase in the proportion of metastatic prostate cancer patients opting for radical prostatectomy as first-line treatment, from 10.0% in 1988-1992 to 32.7% in 1998-2003 and a concomitant decline in men receiving other types of cancer-directed surgeries.

Among men with distant metastases at diagnosis, the study revealed an upward shift in the proportion of patients not receiving any type of cancer-directed surgery (from 67.4% in 1988-1992 to 88.9% in 1998-2003).

“Based on advances in screening and diagnostic techniques,” the authors wrote, “it is likely that at least a portion of individuals are being diagnosed earlier in the disease process and are therefore surviving longer; but improvements may also be credited to increasingly successful treatment options for patients with advanced disease.”

The researchers said their study has important clinical implications. “As younger men may expect to live longer with advanced disease, long-term management of their condition must be carefully planned, particularly with respect to quality of life.”