Asians in U.S. Have Better Prostate Cancer Survival Despite Worse Risks

SACRAMENTO, Calif., Aug. 13 -- The Asian factor in better prostate cancer survival remains unexplained, investigators here reported.

Despite poorer prognostic profiles, men from most areas of Asia living in the U.S. have a survival advantage over U.S. whites, reported Anthony Robbins, M.D., Ph.D., of the California Cancer Registry, and colleagues, online in advance of the in the Sept. 15 issue of Cancer.

Four of six Asian subgroups -- Japanese, Chinese, Korean, and Filipino -- had a significantly lower mortality risks compared with whites. The survival advantage existed even though all six subgroups had demographic and clinical characteristics that should have put them at a survival disadvantage.

"These results argue that traditional prognostic risk factors for survival from prostate cancer do not explain why the majority of Asian men have better survival compared with whites," concluded Dr. Robbins and colleagues.

Only the findings for South Asian men were intuitive, the authors stated, demonstrating both a poorer risk factor profile and poorer survival compared with whites.

The findings came from an analysis of prostate cancer data from the California Cancer Registry. Citing a lack of information about prostate cancer survival in Asian subgroups, Dr. Robbins and colleagues extracted data on all men diagnosed with prostate cancer during 1995 through 2004 and followed through 2004.

The resulting study population of 116,916 men consisted of non-Hispanic whites and six subgroups of Asians: Japanese, Chinese, Korean, Vietnamese, Filipino, and South Asian. The groups were evaluated with respect to prognostic factors (age, summary stage, primary treatment, histologic grade, socioeconomic status, and year of diagnosis) and prostate cancer survival.

Each of the prognostic factors differed significantly between the whites and Asian subgroups, and all six Asian subgroups had risk-factor profiles that placed them at a survival disadvantage compared with Caucasians.

The entire study group had a 10-year risk of prostate cancer mortality of 11.9%. In unadjusted analyses, Japanese men had significantly lower mortality compared with white men (8.1% versus 12%, hazard ratio 0.66). South Asian men had significantly higher mortality compared with whites (16.4%, HR 1.40), and the remaining four Asian subgroups had equivalent mortality to white men (9.8% to 11.3%).

In multivariate analyses that adjusted for baseline differences in prognostic factors, four Asian subgroups had significantly lower mortality compared with the Caucasians, with hazard ratios ranging from 0.49 for Japanese men to 0.60 for Korean men. Vietnamese men (HR 0.68) and South Asians (HR 1.10) had a prostate cancer mortality risk that did not differ significantly from that of whites.

In an attempt to eliminate confounding by key prognostic factors, Dr. Robbins and colleagues performed additional analyses comparing the five non-South Asian groups and whites within quintiles of histologic grade, summary stage, primary treatment, and socioeconomic status. For all four prognostic factors, the Asian subgroups had better survival compared with whites.

The reasons for the survival disparities are unknown, but several explanations have been offered, the authors stated: racial differences in endogenous hormones, dietary factors, and body composition. These are the same explanations proffered for differences in prostate cancer incidence among Asians and whites.

The discordant results between South Asian men and the other Asian subgroups are consistent with findings from previous studies of breast cancer and prostate cancer, the authors noted.