Continued Enzalutamide Strategy Fails to Benefit mCRPC

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Patients with mCRPC saw no decrease in overall PSA progression risk if enzalutamide is continued and abiraterone/prednisone was added.
Patients with mCRPC saw no decrease in overall PSA progression risk if enzalutamide is continued and abiraterone/prednisone was added.
The following article features coverage from the 2017 American Society of Clinical Oncology Annual Meeting in Chicago, Illinois. Click here to read more of Oncology Nurse Advisor's conference coverage. 

CHICAGO—Men with chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC) who experience PSA progression while on enzalutamide do not experience a decrease in overall progression risk if enzalutamide is continued and abiraterone/prednisone is added to treatment, investigators reported at the 2017 American Society of Clinical Oncology (ASCO) Annual Meeting. The combined treatment, however, may delay radiographic progression.

As part of the phase 4 PLATO trial, Gerhardt Attard, MD, of The Institute of Cancer Research and The Royal Marsden Hospital in Sutton, United Kingdom, and colleagues evaluated the safety and efficacy of continued enzalutamide therapy plus abiraterone/prednisone versus placebo plus abiraterone/prednisone. The investigators enrolled 509 patients in Period 1. In this part of the study, men received enzalutamide at a dose of 160 mg; men with no PSA increase from baseline at week 13 and 21 continued treatment until PSA progression, defined as a 25% or greater increase and a PSA rise of 2 ng/mL or higher above nadir. At data cutoff (October 7, 2016), 84 patients were active, 174 had discontinued, and 251 entered Period 2.

Dr Attard's group randomly assigned eligible men in Period 2 to enzalutamide plus abiraterone/prednisone (1000 mg/10 mg) or placebo plus abiraterone/prednisone. The primary end point was progression-free survival (PFS, radiographic or unequivocal clinical progression, or death on study) in Period 2. The median treatment duration in Period 2 was 5.6 months in both treatment arms. Radiographic, clinical, and death PFS event rates were 38%, 25%, and 2%, respectively, for the enzalutamide group and 55%, 18%, and 1% for the placebo group, respectively. Median PFS was 5.7 months for the enzalutamide patients and 5.6 months for placebo recipients. “Continuing enzalutamide after addition of abiraterone and [prednisone] post-PSA progression on enzalutamide did not result in a statistically significant improvement in progression-free survival,” Dr Attard told colleagues.

The median time to PSA progression was 2.8 months for both study arms. The median radiographic PFS, however, was longer in the enzalutamide arm than the placebo arm (10 months vs 7 months). “Sensitivity analysis for radiographic progression-free survival showed a nominally significant difference, but this may be subject to multiple biases,” Dr Attard said.

Read more of Oncology Nurse Advisor's coverage of the 2017 American Society of Clinical Oncology Annual Meeting by visiting the conference page.

Reference

1. Attard G, Borre M, Gurney H, et al. A phase IV, randomized, double-blind, placebo (PBO)-controlled study of continued enzalutamide (ENZA) post prostate-specific antigen (PSA) progression in men with chemotherapy-naïve metastatic castration-resistant prostate cancer (mCRPC). Oral presentation at: 2017 American Society of Clinical Oncology Annual Meeting; June 2-6, 2017; Chicago, IL.

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