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Schematic representation of trial design, patient recruitment, arm assignment, and assignment to endpoint investigations.

Interim analysis of Grade {greater than or equal to}3 hematologic toxicity in the first 10 patients recruited to the combination arm (radium-223 + enzalutamide).

Trial Protocol

Purpose:Radium-223 is approved for metastatic castration-resistant prostate cancer (mCRPC) based on improved overall survival, and delay in skeletal related events. However, it is not associated with PSA or radiographic response, which poses a challenge in real-time assessment of its efficacy. Surrogate markers of treatment outcomes may facilitate tailoring treatment duration with radium-223, by limiting the duration of therapy with radium-223 in these patients. Here, we sought to investigate the utility of bone metabolic markers (BMMs) as surrogate markers of response to radium-223 in mCRPC.Patients and Methods:A prospective phase II trial of radium-223 plus enzalutamide (RE) versus enzalutamide alone was designed to assess surrogacy of BMMs with respect to response to radium-223. Enzalutamide was used as a comparator in lieu of placebo due to the progressive disease. Co-primary endpoints were relative change in serum BMM N-telopeptide (NTP) levels from baseline to 6 months between the two arms and safety and feasibility of the combination.Results:Thirty-nine men were randomized to RE (n = 27) or enzalutamide (n = 12). Combination was safe and feasible. Primary endpoint was met. A statistically significant relative change to NTP ratios between arms (0.64, 95% confidence interval, 0.51–0.81; P = 0.00048) favored RE versus enzalutamide. Overall, BMMs decreased with the RE therapy compared with enzalutamide. Improved PSA response rate in RE versus enzalutamide (P = 0.024), correlated with decline in BMMs.Conclusions:BMMs declined significantly with combination therapy, and were associated with improved outcomes. Upon external validation, BMMs may emerge as surrogate markers to monitor treatment with radium-223 in real-time.

Time to nadir for BMMs and PSA.

Purpose: Radium-223 is approved for metastatic castration-resistant prostate cancer (mCRPC) based on improved overall survival, and delay in skeletal related events. However, it is not associated with PSA or radiographic response, which poses a challenge in real-time assessment of its efficacy. Surrogate markers of treatment outcomes may facilitate tailoring treatment duration with radium-223, by limiting the duration of therapy with radium-223 in these patients. Here, we sought to investigate the utility of bone metabolic markers (BMMs) as surrogate markers of response to radium-223 in mCRPC. Patients and Methods: A prospective phase II trial of radium-223 plus enzalutamide (RE) versus enzalutamide alone was designed to assess surrogacy of BMMs with respect to response to radium-223. Enzalutamide was used as a comparator in lieu of placebo due to the progressive disease. Co-primary endpoints were relative change in serum BMM N-telopeptide (NTP) levels from baseline to 6 months between the two arms and safety and feasibility of the combination. Results: Thirty-nine men were randomized to RE (n = 27) or enzalutamide (n = 12). Combination was safe and feasible. Primary endpoint was met. A statistically significant relative change to NTP ratios between arms (0.64, 95% confidence interval, 0.51–0.81; P = 0.00048) favored RE versus enzalutamide. Overall, BMMs decreased with the RE therapy compared with enzalutamide. Improved PSA response rate in RE versus enzalutamide (P = 0.024), correlated with decline in BMMs. Conclusions: BMMs declined significantly with combination therapy, and were associated with improved outcomes. Upon external validation, BMMs may emerge as surrogate markers to monitor treatment with radium-223 in real-time.

125 Background: RA, a bone targeting alpha radiopharmaceutical, and EZ, are approved for mCRPC. Per phase 3 SWOG0421 trial, men with mCRPC and a significant decline in serum bone metabolism markers (BMM) had improved survival with atrasentan, a bone targeting agent (PMID 24565955). We hypothesized that RA+EZ is safe, and decrease bone metabolism markers compared to EZ alone. Here we report the long-term follow up of the secondary clinical endpoints. Methods: In this phase 2 trial (NCT02199197), men with progressive mCRPC were treated with EZ (160 mg daily) ± RA (standard dose of 55 kBq/kg IV Q4 weeks x 6), until disease progression or unacceptable toxicities. Primary objectives: 1) changes in N-telopeptide compared from baseline to end of treatment; 2) safety. Secondary objectives: changes in 4 other markers of bone resorption or formation, and PSA progression free survival (PSA-PFS), radiographic PFS (rPFS) and overall survival (OS). Results: After a safety lead in phase (n=8), 39 men were randomized (2:1) to RA+EZ vs EZ. Median follow up is 19.3 months (range 3 – 24 months). Combining RA+EZ was safe (2018 ASCO annual meeting abstract: 5057) and met the primary endpoint (2018 ESMO annual meeting: Annals of Oncology). There was a consistent trend regarding PSA-PFS, rPFS and OS favoring RA+EZ over EZ. . . (Table). Notably, no bone fractures have occurred in either group with extended follow up. Conclusions: The use of RA+EZ was safe with a longer follow up with no increase in skeletal related events including fractures. All secondary endpoints, numerically favored RA+EZ vs EZ. Clinical trial information: NCT02614859.

5057Background: Ra-233, a bone targeting alpha radiopharmaceutical, and Enza, are approved for mCRPC. Per SWOG0421, the subset of men with mCRPC with the highest bone metabolism marker levels had i...