THE PSA NADIR THAT INDICATES POTENTIAL CURE AFTER RADIOTHERAPY FOR PROSTATE-CANCER

Objectives. The prostate-specific antigen nadir that indicates potenti al cure by radiotherapy has never been established. We determined this nadir level and used it to define precisely disease freedom after rad iotherapy. Methods. Combination radioactive I-125 prostate implant fol lowed by external-beam radiation was administered to 660 men with clin ical Stage T1T2NO prostate cancer. The average pretreatment prostate-s pecific antigen level (Tandem R Assay) was 11.7 ng/mL (median 8.0 ng/m L, range 0.3 to 188 ng/mL). To analyze these data, recurrence was defi ned as a prostate-specific antigen level rising above whatever nadir w as achieved. The median follow-up is 42 months (range 12 to 150 months ). Results. Eighty-one percent of all men are calculated to achieve a prostate-specific antigen nadir of 0.5 ng/mL or less and to have a 5- and 10-year disease-free survival rate of 93% and 85%, respectively, a s compared with a 5-year disease-free survival rate of 26% for those a chieving a nadir of 0.6 to 1.0 ng/mL-a significant difference (P = 0.0 001). All men with a nadir greater than 1.0 ng/mL ultimately failed tr eatment. Of 201 men with a minimum 5-year follow-up, 143 are disease-f ree and 140 (98%) achieved and maintained a nadir of 0.5 ng/mL or less . Conclusions. For possible cure of prostate cancer with radiotherapy, a prostate-specific antigen nadir of 0.5 ng/mL or less should be achi eved. With this nadir level, disease freedom after irradiation is defi ned as achievement and maintenance of a nadir of 0.5 ng/mL or less. A nadir greater than 0.5 ng/mL or subsequent increase above 0.5 ng/mL is defined as irradiation treatment failure. This definition may help re solve the controversy about the potential for cure of prostate cancer by irradiation. (C) 1997, Elsevier Science Inc.