Abstract B57: Cabozantinib (XL184) reduces pain symptoms in patients (pts) with castration-resistant prostate cancer (CRPC) and bone metastases: Results from a phase 2 nonrandomized expansion cohort.

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Abstract Background: Cabozantinib is a potent inhibitor of MET and VEGFR2. Cabozantinib treatment (100 mg qd) of CRPC pts in a Phase 2 randomized discontinuation trial resulted in high rates of both disease control per RECIST and resolution of bone lesions on bone scans. In addition, the majority of pts with bone metastases and pain at baseline experienced pain improvement per post-hoc investigator survey. Based on these data, a non-randomized expansion cohort was initiated for CRPC pts that included prospective evaluation of changes in pain and analgesic use. Methods: Eligible pts had CRPC metastatic to the bone and had progressed on prior docetaxel therapy. Pain at baseline was not required for study entry. Cabozantinib was administered open label at 100 mg free base equivalent qd, and pain and analgesic use were evaluated daily over 7-day assessment intervals at baseline and during Weeks 3, 6, 12, and every 6 weeks thereafter. Using an interactive voice-response system (IVRS) questionnaire, pts rated pain at its worst over the prior 24 hours on a scale of 0–10 (0=no pain, 10=pain as bad as you can imagine), and interference with sleep and daily activity caused by pain using items from the Brief Pain Inventory. Pts also rated pain at its worst relative to the most recent prior assessment. Daily analgesic use was self-reported by pt diary. Of 100 planned patients, 51 have been enrolled and are evaluable for pain changes in this interim analysis. Results: For the 51 enrolled pts with a minimum of 6 weeks of follow-up, evaluable data were obtained for 183/201 (91%) assessment intervals. Changes in average worst pain are summarized in Table 1. Among the 23 pts that had average daily worst pain at baseline ≥4, 20 reported regular use of narcotic analgesics during the baseline assessment interval. Changes in sleep and daily activity, as assessed by pain interference questions, were generally consistent with the effects observed in pain. Conclusions: Docetaxel-pre-treated CRPC pts with bone metastases treated with cabozantinib completed IVRS pain questionnaires with a high rate of compliance (>90%) in this prospective analysis. High rates of pain reduction that was often accompanied by a concomitant decrease in narcotic use were observed in pts with baseline pain, consistent with prior retrospective analyses. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B57.