THE EFFECT OF PELVIC RADIATION-THERAPY ON SERUM LEVELS OF PROSTATE-SPECIFIC ANTIGEN

To determine the effect of prostatic irradiation on the production of prostate specific antigen (PSA), serum PSA levels were measured in 36 men who received pelvic irradiation (45 to 65 Gy.) for nonprostatic ma lignancies, and compared with those of a control group of 79 men of co mparable age without prostate cancer or prior pelvic irradiation ident ified from the records of the Massachusetts General Hospital internal physicians. The median PSA level was lower in the irradiated group tha n in the control group (0.65 versus 1.1 ng./ml.). Of the irradiated pa tients 47% had undetectable PSA levels versus 20% of the controls (p = 0.004, Fisher's exact test). A group of 27 prostate cancer patients w ho received up to 68 Gy. 8 to 16 years (median 10 years) previously an d who remained clinically disease-free were also studied. The median P SA level was less than 0.5 ng./ml. The proportion of patients with und etectable PSA levels was significantly higher than that of the control s (p <0.001) but it was not significantly different from those irradia ted for other pelvic cancers. Of those patients 67% had an undetectabl e PSA level and 78% had a level of less than 1 ng./ml. Our study sugge sts that radiation therapy results in a permanent decrease in PSA prod uction by the prostate gland and that patients whose PSA values do not reach less than 1 ng./ml. following radical radiation therapy for pro state cancer are unlikely to be long-term clinical disease-free surviv ors.