Targeted therapy shows anti-tumor activity in advanced prostate cancer

A novel androgen receptor antagonist known as MDV3100 appears to show durable anti-tumor activity in castration-resistant prostate cancer patients as measured by PSA declines, radiographic findings, circulating tumor cell changes, and time on treatment, according to an ongoing phase I-II trial.

MDV3100 has been generally well tolerated, with no reports of serious treatment-related adverse events, researchers say.

The open-label, dose-escalation study includes prostate cancer patients who have failed standard hormonal therapies. To date, 120 patients have been enrolled in the trial with enrollment completed at doses up to 360 mg/day. A total of 73 patients in the three lowest expanded dose groups (60, 150, and 240 mg/day) have been followed for more than 24 weeks. Of these, 31 patients (42%) have surpassed 24 weeks.

At 12 weeks, 36 of 73 patients (49%) had a more than 50% decline in PSA from baseline. Patients also saw improvements as measured by radiographic changes and reductions in the number of circulating tumor cells, including 38% of patients with evaluable soft tissue lesions in the 240 mg/day cohort showing a partial response at 24 weeks.

The data suggest a dose-response trend, with a higher percentage of patients in the 240 mg/day cohort experiencing 90% reduction in PSA levels, radiographic partial responses, and conversions to favorable circulating tumor cell counts of less than five post-treatment.

The findings were presented at the EORTC-NCI-AACR Molecular Targets and Cancer Therapeutics symposium in Geneva.