LOCALIZED PROSTATE-CANCER - USE OF SERIAL PROSTATE-SPECIFIC ANTIGEN MEASUREMENTS DURING RADIATION-THERAPY - AN UPDATE

Background: Serum prostate-specific antigen (PSA) has proven to be the most useful tumor marker for prostate cancer. We previously reported the decline rate of PSA levels in patients with cancer of the prostate during radiotherapy; however, on the basis of a small number of patie nts, no definite conclusions were drawn. Material and Methods: In this report, we update our findings from a prospective study in which chan ges in PSA levels during radiotherapy (RT) were determined. Pre-RT and weekly PSA levels during 7-8 weeks of RT were measured in 76 stage A- C patients with prostate cancer. Results: In a majority (78%) of patie nts, the PSA levels declined. The mean rate of PSA decline was 1.3%/da y or about 9%/week during RT. 13 patients received hormonal therapy pr ior to RT; their mean rate of decline (1.8%/day) was not significantly different from the average rate in 63 patients who had no hormonal tr eatment (1.2%/day). 11 patients had one or more digital rectal examina tions (DRE) during the RT course; the mean rate of PSA decline (0.5%/d ay) was significantly less than the mean rate of decline in 65 patient s who had no DRE (1.5%/day; p=0.033); however, the median rates of dec line between these groups were not statistically different. There was a significant (p=0.0004) transient increase in the PSA values 24 h aft er the first RT fraction. No significant association was found between rate of decline and age, stage, grade, or race in the group of patien ts with no hormonal therapy. Tumor volume was calculated from prostate volume and initial PSA level prior to RT; a highly significant correl ation was found between tumor volume and the rate of decline (p<0.001) . In a multivariate model which included age, stage, grade, race and t umor volume, the latter remained significantly associated (p<0.001) wi th the rate of PSA decline, A similar univariate and multivariate anal ysis showed that PSA density also was associated with the rate of PSA decline during RT (p<0.001). Conclusion: The rate of PSA decline durin g RT is associated with the calculated tumor volume; PSA density is al so similarly correlated with the rate of PSA decline. Our findings can be interpreted to mean that prostate cancer cells may be more radiose nsitive than non-malignant prostate cells. Whether the rate of PSA dec line during RT can predict subsequent outcome is not known at this tim e.