Oncology

Prostate Cancer

Assessing Rapid Treatment Response in First-Line Metastatic Castration-Resistant Prostate Cancer (mCRPC)

clinical study insights by Oliver Sartor, MD

Overview

Clinical Study Title:
Early Assessment of PSA Response in Patients With mCRPC Treated With Enzalutamide and Abiraterone

Clinical Study Abstract:
While resistance to abiraterone and enzalutamide in patients with metastatic castrate-resistant prostate cancer (mCRPC) has been well documented, little data exist on rates of rapid treatment response. Feibus et al conducted a single-institution retrospective review of PSA response in 123 mCRPC patients treated with abiraterone or enzalutamide.

A PSA response was achieved in 52/123 (42%) of patients taking abiraterone, with median time to PSA nadir of 37 days. Fifty-eight percent of patients responded to the drug within 4 weeks. PSA response to enzalutamide was achieved in 21/123 (17%) of patients, with a median time to PSA nadir of 140 days. Eighty-six percent of patients responded to the drug within 4 weeks.

The authors conclude that time to drug response and achievement of PSA decline can help predict long-term PSA response in patients with mCRPC.

Reference:
Feibus AH, Guccione JR, Vasudevamurthy A, et al. Early assessment of PSA response in patients with mCRPC treated with enzalutamide and abiraterone. J Clin Oncol. 2017;35 (suppl 6S; abstract e574).

Expert Commentary

Oliver Sartor, MD

C. E. and Bernadine Laborde Professor of Cancer Research
Medical Director, Tulane Cancer Center
Associate Dean for Oncology
Tulane University School of Medicine
New Orleans, LA

In Abstract e574, published at the 2017 American Society of Clinical Oncology Genitourinary Symposia by Feibus et al, a series of patients were analyzed for the rate of PSA decline after beginning abiraterone or enzalutamide. The patients were analyzed every 4 weeks rather than every 3 months as in the original phase 3 trials with these agents. For abiraterone, 68% of the patients who eventually responded with a 50% PSA decline had that 50% decline within 4 weeks. With enzalutamide, of the patients who responded to the drug, 86% responded within 4 weeks.

The easiest way to interpret these data are that a response to enzalutamide, as measured by a 50% PSA decline, can be determined in the vast majority of patients after only 4 weeks on therapy. The data on abiraterone, however, are not nearly as reliable at 4 weeks.

Additional data on early PSA declines (>50% decline) have been reported in abiraterone-treated patients by Facchini and colleagues (Front Pharmacol. 2016;7:123). They reported an early PSA response in 56% of patients evaluated at Day 15, and furthermore found that both progression-free survival and overall survival were improved for those with an early response.