Prostate specific antigen nadir achieved by men apparently cured of prostate cancer by radiotherapy

Purpose: The role of prostate specific antigen (PSA) nadir in the definitio n of disease freedom after radiotherapy of prostate cancer is controversial . We evaluate post-irradiation PSA nadir in men apparently cured of this di sease. Materials and Methods: From 1984 to 1993, 354 men with clinical stage T1T2N 0 prostate cancer were treated with radioactive (125)iodine prostate implan t followed by external beam radiation. Median pretreatment PSA was 8.4 ng./ ml. (range 0.3 to 188). Of these men 250 are disease-free and median pretre atment PSA was 6.5 ng./ml. (range 0.3 to 123). Treatment failure is defined as 3 consecutive PSA increases above nadir. Median followup is 7 years (ra nge 5 to 14 years) for the 250 disease-free men and 6 years (range 0.5 to 1 4) for all 354 men. Results: PSA nadir 0.5 ng./ml. or less was achieved by 98% of all disease-f ree men (244 of 250) with minimum 5-year followup, including 87% (217) who achieved nadir 0.2 ng./ml. or less. All 27 disease-free men with minimum 10 -year followup had a PSA nadir of 0.5 ng./ml. or less. PSA nadir significan tly correlated with disease-free survival by receiver operator characterist ics curve analysis (0.93 area under the curve) in all 354 men. Conclusions: PSA nadir is the fundamental measurement that determines possi ble cure after radiotherapy. Except for perhaps rare occasions, men must at least achieve a nadir of 0.5 ng./ml. or less to be cured of prostate cance r by irradiation, However, the prognostic value of this nadir level depends on most men achieving a nadir of 0.2 ng./ml. or less. Disease freedom for radiotherapy, defined as achievement and maintenance of PSA nadir 0.5 ng./m l. or less, is reasonable.