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Clovis Oncology Shows Positive Initial Phase 2 Data in Prostate Cancer

44% confirmed objective response rate in metastatic castration resistant prostate cancer. Rubraca (rucaparib) is FDA approved as maintenance treatment for ovarian cancer. (Image: Clovis Oncology)

~ 44% confirmed objective response rate in metastatic castration resistant prostate cancer. Rubraca (rucaparib) is FDA-approved for the maintenance treatment of adults with recurrent ovarian cancer who are in complete or partial response to platinum-based chemotherapy. ~

Prostate cancer is the second most commonly occurring cancer in men in the US, after only skin cancer. About 164,690 new cases of prostate cancer will be diagnosed in 2018, according to the American Cancer Society, and about 29,430 deaths this year will be attributable to prostate cancer. About 1 out of 9 men will be diagnosed with prostate cancer during his lifetime.

According to the American Urological Association, deaths from prostate cancer are typically the result of the subtype known as metastatic castration-resistant prostate cancer (mCRPC), in which the cancer grows despite very low levels of testosterone in the body. The median survival for men with mCRPC historically has been less than two years, and the five-year survival rate is approximately 29%.

Boulder, Colorado, based Clovis Oncology CLVS announced initial results from its ongoing Phase 2 trial of Rubraca (rucaparib) in male adults with mCRPC at the European Society for Medical Oncology (ESMO) 2018 Congress in Berlin. The data showed a confirmed objective response rate (ORR) of 44% and a prostate specific antigen (PSA) response rate of 51% in patients with a BRCA1 or BRCA2 alteration. Reductions in target lesion diameters and PSA measurements have also been observed in patients with an ATM alteration.

Rubraca has previously demonstrated antitumor activity in its approved indications for women with advanced ovarian cancer. These new data show that Rubraca may also offer a new approach for the treatment of mCRPC associated with BRCA1 and BRCA2 alterations, with the potential to achieve a clinical response in patients with few remaining therapy options.

– Wassim Abida, MD, PhD, Medical Oncologist, Memorial Sloan Kettering Cancer Center, and principal investigator for the Phase 2 study.

Rubraca is an oral, small molecule inhibitor of PARP1, PARP2 and PARP3 (poly ADP ribose polymerase) that is being developed in multiple tumor types, including ovarian, metastatic castration-resistant prostate, and bladder cancers, as monotherapy, and in combination with other anti-cancer agents. Inhibiting PARP may prevent cancer cells from repairing their damaged DNA. The drug is FDA approved for (i) the maintenance treatment of adults with ovarian cancer, fallopian tube cancer, or primary peritoneal cancer whose cancer has come back and who are in complete or partial response to a platinum-based chemotherapy, and (ii) the treatment of adults with those cancers who have certain BRCA mutations and who have been treated with at least two chemotherapies. BRCA1 and BRCA2 are genes that produce tumor suppressor proteins. The ATM gene produces a protein found primarily in cell nuclei, helping control the rate at which cells grow and divide. Mutations or alterations in these genes cause disruption to those functional proteins that can lead to cancer.

These study results were the basis for the FDA’s Breakthrough Therapy designation, granted on October 2, 2018, for Rubraca as a monotherapy treatment of adult patients with BRCA1/2 mutated mCRPC who have received at least one prior androgen receptor-directed therapy and taxane-based chemotherapy which was granted on October 2, 2018 by the U.S. Food and Drug Administration (FDA).

We are very encouraged by these initial findings from the TRITON2 study, which demonstrate the potential of Rubraca to treat men with advanced prostate cancer whose disease has progressed after receiving multiple prior lines of therapy. PARP inhibitors are now a validated therapeutic class in oncology in multiple tumor types, and these new data underscore the benefit that Rubraca may provide for men with advanced, BRCA-mutant castration-resistant prostate cancer. Having recently received Breakthrough Therapy designation based on these data, we are committed to the rapid development of Rubraca for men with this very difficult-to-treat disease.

– Patrick J. Mahaffy, President and CEO, Clovis Oncology.

Shares in Clovis are down 60% on the year, against the grain of most stocks in the sector, as investors appear to be disappointed with sales of Rubraca to date. The latest data presented at ESMO may turn investor sentiment, however, as the FDA’s Breakthrough Therapy designation positions Rubraca as possibly the first PARP inhibitor that may be approved to treat prostate cancer.

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