A prostate-specific antigen (PSA) nadir level of up to 1 ng/mL after three-dimensional conformal radiotherapy for patients with localized prostate cancer is a powerful prognostic variable, according to Dr. Michael Zelefsky of the Department of Radiation Oncology at Memorial Sloan-Kettering Cancer Center in New York City. In addition, such levels impact upon PSA relapse-free survival and predict local control.
A total of 743 patients with localized prostate cancer were treated at the Memorial-Sloan Kettering Cancer Center with conformal radiotherapy. To analyze the impact of PSA nadir after therapy, 530 patients were studied who did not receive neoadjuvant hormonal therapy as part of their treatment. Of these 530 patients, 40% had stage T2C or T3 prostate cancer and the remaining 60% had stage T1 through T2B. The median follow-up was 27 months. The breakdown of pretreatment PSA levels follows: 45% of patients had PSA levels of between 1 and 10 ng/mL; 31% of patients had PSA levels of between 10 and 20 ng/mL; and 24% of patients had PSA levels of higher than 20 ng/mL.
The variables that predict PSA relapse were evaluated. Although the definition of PSA relapse used in this study was two consecutive PSA level rises from the nadir levels, the investigators are readjusting this definition to three consecutive rising PSA levels above the nadir value, based on the modification proposed at the San Antonio Consensus Conference. Although three variables--a PSA level higher than 10 ng/mL, a Gleason score of at least 7, and clinical stage T3 disease--were found to be predictive of PSA relapse, the PSA nadir level was the strongest predictor, overshadowing the significance of the pretreatment PSA level.
Regarding PSA relapse-free survival based on PSA nadir levels, a dramatic difference was seen between patients who achieved PSA nadir levels of up to 1 ng/mL and patients who achieved PSA nadir levels of higher than 1 ng/mL; 93% of patients with PSA nadir levels of between 0 and 0.4 ng/mL after radiotherapy had PSA relapse-free survival at 3 years, compared with 81% of patients with PSA nadir levels of between 0.5 and 1.0 ng/mL.
In addition to pretreatment PSA levels of up to 10 ng/mL and the stage of disease, radiation doses of 75.6 Gy and higher significantly increased the likelihood of achieving PSA nadir levels 1 or less ng/mL. Furthermore, patients with PSA nadir levels of 1 or less ng/mL had a significantly lower positive biopsy rate after treatment than did patients with higher PSA nadir values. Based on the biopsy data obtained after radiotherapy, PSA nadir levels 1or less ng/mL with a nonrising PSA level profile appears to be the most predictive variable of local tumor control.