Androgen deprivation for minimal metastatic disease: threshold for achieving undetectable prostate-specific antigen.

OBJECTIVES: To develop objective measures to select systemic therapies for study in large-scale trials for patients with lesser tumor burdens, we explored prostate-specific antigen (PSA) changes after androgen ablation in patients with disease progression after treatment of localized disease. Long-term follow-up of trials incorporating androgen-deprivation with local therapy have shown improved survival relative to local therapy alone. This suggests that the benchmark for treatment of minimal metastatic disease can be cure.
METHODS: Patients with a rising PSA level with or without clinical metastases after local therapy who received androgen deprivation at Memorial Sloan-Kettering Cancer were identified from two institutional databases. The primary outcome was the proportion achieving an undetectable PSA level, and the pretreatment parameters associated with this endpoint were evaluated.
RESULTS: A total of 130 patients who received androgen ablation and were followed up at Memorial Sloan-Kettering Cancer Center were identified. Overall, 31 (57%) of 54 (95% confidence interval 44% to 71%) patients with a rising PSA level alone and 28 (37%) of 76 (95% confidence interval 26% to 47%) patients with a rising PSA level and clinical metastases achieved an undetectable PSA level after androgen ablation (P = 0.02). The PSA level at the start of androgen ablation and the presence of metastases were the most significant predictive factors.
CONCLUSIONS: The probability of achieving an undetectable PSA level varied inversely with the disease extent. Although achieving an undetectable PSA level does not mean that a patient has been cured, it does establish an endpoint that can be used to identify approaches worthy of study in the Phase III setting.