Paradoxical significance of endorectal MRI (erMRI) response to neoadjuvant chemotherapy in patients with high-risk localized prostate cancer (HRLPC).

23 Background: Intermediate endpoints are desirable to expedite the integration of perioperative systemic therapy in HRLPC. erMRI response has been utilized as an endpoint in neoadjuvant trials but has not been correlated with clinical outcomes. Methods: Data were pooled from two trials exploring neoadjuvant chemotherapy in HRLPC. Trial 1 explored docetaxel for 6 months and Trial 2 explored docetaxel plus bevacizumab for 4.5 months, both prior to radical prostatectomy (RP). erMRI was done at baseline and end of chemotherapy. erMRI response was categorized as PR (>50% decline in largest lesion), MR (25%-50% decline), or no response. PSA response was defined as >50% decline in PSA compared to baseline. Multivariable Cox regression was undertaken to evaluate the association between clinical parameters and biochemical recurrence (BCR). Results: Trial 1 enrolled 19 patients and Trial 2 enrolled 41 patients. Among the 60 evaluable patients in the combined analysis, 20 (33%) achieved a PSA response, 16 (27%) ach...