The impact of irregularly rising prostate-specific antigen and “impending failure” on the apparent outcome of localized prostate cancer following radiotherapy

Abstract

Purpose: To examine the impact of irregularly rising prostate-specific antigen (PSA) and “impending” biochemical failure on the apparent rate of biochemical relapse following radiotherapy for localized prostate cancer. Methods and Materials: We analyzed the outcome of 572 patients with T1/T2 prostate cancer treated with radiotherapy alone at the Princess Margaret Hospital (median follow-up, 4.21 years). Biochemical outcomes were analyzed using 2 different definitions of failure: ( 1) the American Society for Therapeutic Radiology and Oncology (ASTRO) definition, and ( 2) a modified definition that included 2 consecutive rises in PSA, with a minimum rise of 1.5 ng/mL above the nadir, or a nadir value of greater than 4 ng/mL. Patients were defined as having “impending failure” when the last 2 PSA measurements taken demonstrated 2 consecutive rises. Results: Two-hundred and thirty patients (40%) met the ASTRO definition of failure; 258 patients (48%) failed by the modified definition ( p = 0.001). Five-year biochemical relapse-free rate (bNED) rate was 55% using the ASTRO definition, and 49% using the modified definition. This difference in 5-year bNED was greatest for patients with high-risk disease (ASTRO definition 30% vs. modified definition 15%). Twenty-four of the 38 additional cases identified as biochemical failures by the modified definition had irregularly rising PSA levels; 14 were “impending failures.” These additional 38 patients had a median PSA elevation 5.4 ng/mL above the nadir, and a high risk of subsequent clinical failure (4-year clinical failure-free rate of 63%). The ASTRO definition had a sensitivity of 87% and specificity of 74% for predicting clinical relapse. The modified definition had a sensitivity of 95% and a specificity of 70%. Conclusion: A definition of biochemical failure that includes an absolute allowable rise in PSA above the nadir can identify patients with rising PSA who are at substantial risk of clinical relapse, but who are not defined as biochemical failures by the ASTRO definition. This is particularly true for patients with high-risk disease. The use of a uniform definition of biochemical failure is crucial to ensure that differences in apparent outcome are not due to differences in the definition of relapse. Currently, the ASTRO definition should remain the standard. Large cohort studies with long follow-up can be utilized to optimize the definition of biochemical failure following radiotherapy for prostate cancer.