Hazard Rates of Disease Progression After External Beam Radiotherapy for Clinically Localized Carcinoma of the Prostate

Abstract

We established hazard rates for disease progression at different intervals after external beam radiotherapy alone in patients with clinically localized prostate cancer. We determined the likelihood of biochemical failure in those free of disease 5 years after radiotherapy and identified those at risk for early versus late biochemical failure. We reviewed the records of 964 patients treated with full dose external beam radiotherapy alone for T1 to T4, NxM0 prostate cancer. Followup prostate specific antigen (PSA) was measured 3 months after the completion of radiotherapy and every 3 to 6 months thereafter. Yearly hazard rates for biochemical failure were calculated each followup year. Median followup of the whole study group was 48 months. Overall 5 and 10-year biochemical disease-free survival rates were 63.7% and 53.6%, respectively. Patients had a peak overall hazard rate 2 years after treatment. The hazard rate then decreased until year 6, when it increased slightly and remained elevated even at year 10. This late increase in the overall hazard rate was associated with late increases in the hazard rate in men with favorable prognostic factors, namely pretreatment PSA less than 10 ng./ml., Gleason score less than 5, clinical T stage T1 or T2, posttreatment PSA nadir less than 0.99 ng./ml. or radiation dose less than 68 Gy. In 13 of the 307 patients (3.9%) with biochemical failure the failure occurred more than 5 years after initial treatment. The peak risk of biochemical failure is 2 years after radiotherapy. Patients are at slight but persistent risk for biochemical failure more than 5 years after treatment. Hazard rate calculations beyond the median followup of 4 years can underestimate the true hazard.