Agent for mCRPC shows clinically significant benefit

In a phase III study, a drug that blocks production of a protein was associated with a 27% reduction in the risk of death.

Men with metastatic castrate-resistant prostate cancer and a poor prognosis benefited significantly from therapy with the experimental drug custirsen, according to results of a retrospective analysis of the phase III SYNERGY trial presented at the American Society of Clinical Oncology annual meeting in Chicago.

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Men with at least two of five common risk factors for poor prognosis had a lower risk of death when treated with custirsen combined with first-line docetaxel (Taxotere) therapy, compared with docetaxel alone, the analysis found. More than 40% of the patients in the trial had two or more of the risk factors: poor performance status, elevated PSA, elevated lactate dehydrogenase, decreased hemoglobin, and liver metastasis.

The analysis included 984 patients from the SYNERGY trial with complete data. Investigators evaluated the treatment effect separately in the 492 men in the poor-prognosis group and found that it was greater than the effect in the good-prognosis group: The hazard ratio estimate for survival benefit with custirsen was 0.73 for the men with a poor prognosis compared with 1.02 for men with a good prognosis.

NEXT: 27% reduction in risk of death

“The survival benefit was clinically significant-a 27% reduction in the risk of death, which translated to a 3-month increase in median survival, from 14 to 17 months,” said lead investigator Kim Chi, MD, of the University of British Columbia and Vancouver Prostate Centre, Vancouver, BC. He noted that the results are encouraging for patients at risk of poor outcomes who need new treatment options as their cancer becomes resistant to initial therapy.

“There is an ongoing phase III study of custirsen in patients receiving second-line chemotherapy with cabazitaxel [AFFINITY trial] where the hypothesis that custirsen is preferentially beneficial in patients with more resistant and poor-prognosis disease will be further tested,” Dr. Kim said.

OncoGenex Pharmaceuticals, which manufactures custirsen, will meet with the FDA in June to discuss including a co-primary endpoint in the AFFINITY trial to evaluate survival in patients at increased risk for poor outcomes. Results from the trial are expected later this year or early next.

Custirsen is designed to block production of the protein clusterin, which is overexpressed in a number of cancers, including prostate, bladder, lung, and breast, and is associated with treatment resistance, faster cancer progression, and shorter survival. The drug has FDA fast-track designation for metastatic castrate-resistant prostate cancer and non-small cell lung cancer.

Dr. Chi’s institution has received research funding from OncoGenex. He and several of his co-authors have financial or other relationships with several pharmaceutical companies.

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