Women with mutated p53 metastatic breast cancer lived twice as long when treated with Reolysin plus Taxol (paclitaxel) compared to those who received Taxol alone, according to the randomized, IND 213 Phase 2 trial (NCT01656538).

Vanessa Bernstein of the British Columbia Cancer Agency in Vancouver presented the study’s findings in a poster, “A Randomized (RCT) Phase II Study of Oncolytic Reovirus (Pelareorep) plus Standard Weekly Paclitaxel (P) as Therapy for Metastatic Breast Cancer (mBC),” at the American Association for Cancer Research (AACR) 2017 Annual Meeting in Washington, D.C.

“Mutations of the p53 tumor suppressor gene play an increasingly challenging role throughout the life cycle of cancer,” Matt Coffey, MD, president and CEO of Oncolytics, said in a press release. “As breast cancer progresses clinically, p53 mutations become more prominent and negatively impact therapeutic efficacy and overall survival. These data provide evidence that combining Reolysin with paclitaxel may improve survival for this difficult-to-treat, well characterized patient population.”

Reolysin is a proprietary formulation of the human reovirus that replicates specifically inside cancer cells, leading to their death. By releasing specific cancer proteins upon cancer cell death, the virus also induces strong immune responses against the remaining cancer cells.

Oncolytics is evaluating the safety and efficacy of Reolysin in metastatic breast cancer patients in the open-label Phase 2 IND 213 trial. The study — designed and conducted by the Canadian Cancer Trials Group — enrolled 74 patients, 82 percent of whom had mutations in the p53 gene.

P53 is a tumor suppressor protein, meaning that it works to prevent the development of tumors. As a result, many cancers have inactivating mutations in this protein, which allows them to progress. While the study did not meet its primary endpoint of superior progression-free survival, which was 3.78 months and 3.38 months in the treatment and control groups, respectively, researchers saw an unexpected seven-month improvement in overall survival. Patients treated with Taxol alone lived a median of 10.4 months, while those on Reolysin lived 17.4 months.

But the most striking effect was among the 61 patients with p53 mutations who lived for a median of 20.9 months when treated with Reolysin, compared to 10.4 months in the control group.

“The observed survival benefit is very exciting and reinforces the effectiveness and tolerability of Reolysin in patients with mutated p53 metastatic breast cancer, while demonstrating its potential utility in earlier lines of treatment for this difficult-to-treat, high-risk group of patients,” said Andres Gutierrez, MD, chief medical officer of Oncolytics. “These data indicate overall survival is more than doubled for patients when treatment with Reolysin is added to the standard of care and highlight key considerations for the design and execution of a registration study in breast cancer. Our immediate next steps include seeking advice from key opinion leaders and regulators on refining our go-forward regulatory strategy and registration pathway.”