Patients with metastatic prostate cancer whose PSA levels remain high despite initial hormone treatments have historically had poor prognosis, with survival typically in the 1-2 year range. Results of a 40-person clinical trial published in JAMA Oncology show that 13 percent of these patients deemed "hormone refractory" did, in fact, have strong responses to treatment with the next-generation hormonal drug abiraterone acetate, with PSA levels falling from above 4.0 ng/ml to below 0.2 ng/ml. An additional 33 percent of patients showed partial response to the drug, achieving PSA levels between 0.2 and 4 ng/ml.
"We set an especially high bar with our goal of reducing PSA to below 0.2, which is very low, especially for this high-risk population. The trial did not meet its success criteria of six full responders, but we feel that with five full responders and evidence that many more patients also received some benefit from the drug, abiraterone acetate deserves more study in this population," says Thomas W. Flaig, MD, investigator at the University of Colorado Cancer Center and the trial's national primary investigator.
Flaig also points to this trial as important evidence of the evolution of hormone therapy in prostate cancer.
"We used to think that if a patient's cancer progressed despite traditional hormone therapy, that was it for hormone therapy. Now we see that's not the case. It may just be that the first drug wasn't strong enough, or that cancer became hypersensitive to any remaining androgen. Now with drugs like abiraterone we can almost completely cut off a cancer's ability to drive its growth with androgen and we see this drug working even after the initial, standard hormone therapy has failed," Flaig says.
The trial is one of many exploring the use of abiraterone acetate in various prostate cancer settings, including uses earlier in the sequence of treatment, and in patients with less progressed disease.
"This is one of the first studies to focus on this high-risk group of patients with early failure of hormone induction therapy. Seeing this level of response in patients that had previously been dubbed 'hormone resistant' reinforces our hope that this drug will help many kinds of patients in many settings," Flaig says.