Radiographic Progression of mCRPC Without Rising PSA
In a PREVAIL trial post hoc analysis, nearly one fourth of men on enzalutamide had radiographic progression despite non-rising PSA.
Non-rising PSA is a relatively common finding among patients who experience radiographic progression of metastatic castration-resistant prostate cancer (mCRPC) while receiving enzalutamide, investigators reported at the European Society for Medical Oncology 2016 congress in Copenhagen.
In a post hoc analysis of the PREVAIL study, Alan H. Bryce, MD, of Mayo Clinic in Scottsdale, Arizona, and colleagues studied 265 mCRPC patients who experienced radiographic disease progression while receiving treatment with enzalutamide. Of these, 200 (75.5%) had rising PSA levels and 65 (24.5%) did not.
“Anecdotal evidence suggests that many clinicians monitor mCRPC patients with PSA alone,” Dr Bryce told Renal & Urology News. The results indicate that routine imaging should be considered regardless of PSA values.
The median progression-free survival time was 8.3 months in the non-rising PSA group compared with 11.1 months in the rising PSA group, which corresponded to a significant 68% increased risk of progression in the non-rising PSA group, Dr Bryce's group reported. The groups had similar overall survival rates. Patient characteristics at study entry were similar in both groups, including median PSA and presence of visceral metastases.
At the time of progression on enzalutamide, 95 patients had bone-only progression, 164 had soft-tissue-only progression, and 6 had both bone and soft-tissue progression. Among 77 patients with bone-only disease at study entry, 31 (40.3%) also experienced development of soft-tissue disease at progression.
“We feel that these results have practical implications for clinical practice, as well as being hypothesis generating from a research perspective,” Dr Bryce said. “Whether the phenomenon of radiographic progression with non-rising PSA represents a form of tumor evolution requiring a distinct treatment paradigm is a question for future studies.”
The PREVAIL study was a double-blind trial that included 1717 patients with minimally symptomatic or asymptomatic mCRPC who had not received chemotherapy. Investigators randomly assigned patients to receive oral enzalutamide at 160 mg/day (872 patients) or placebo (845 patients).
1. Bryce AH, et al. A post hoc analysis of radiographic progression with nonrising prostate-specific antigen in patients with metastatic castration-resistant prostate cancer (mCRPC) in the PREVAIL study. Data presented at the European Society for Medical Oncology 2016 congress in Copenhagen, May 7-11.. Poster 760P. Ann Oncol 2016;27 (Suppl 6):vi261.