Prima re-evaluating CVac trial design

Prima BioMed (ASX:PRR) is reviewing the design for future trials of its CVac cancer vaccine candidate, because data from a previous trial suggests there won’t be a significant impact on progression-free survival (PFS).

Prima CEO Matthew Lehman and CTO Sharron Gargosky this week gave a presentation detailing some of the results of its CAN-003 phase II trial in epithelial ovarian cancer patients.

Despite some strong results in terms of safety and T-cell activity, the data so far suggests that there won’t be a statistically significant impact on progression-free survival in CVac patients compared to the standard-of-care controls.

According to Lehman, this is a common issue among cancer immunotherapies in clinical trials. The problem is it takes time to prime T-cells to attack cancer cells and if new tumours develop over this time, patients will be classified as progressed even if they later show a complete response.

Although investigators are starting to recognise this and adopt more flexible criteria, regulators still use the old RECIST (response evaluation criteria in solid tumours) criteria to evaluate the success of trials.

Lehman said that while establishing a statistically significant increase in PFS was not necessarily a goal of the CAN-003 trial, its results to date may influence the next study.

“We have suspended the enrolment of new patients on the CAN-004 trial, the CANVAS program. We are reviewing the clinical endpoints for that trial, both immunological and survival endpoints, as that trial was initially designed with PFS as the primary endpoint,” he said.

The company also plans to dramatically reduce the planned number of patients to be enrolled in the study, which could delay the start of the program for a “couple of months” into early 2014.

The patients still enrolled in the CAN-003 study will meanwhile be continuously monitored to evaluate overall survival and the company hopes to be able to identify analysable trends in the data by the end of next year.

“We are a bit disappointed, of course, by the outcome on progression-free survival and the fact that this will increase the time of our clinical trials. Overall, we are very pleased to see the positive activity of CVac on the immune system and the tolerability of the treatment in patients,” Lehman said.

The CAN-003 study involved 63 epithileal ovarian cancer patients in complete first or second remission. The first seven patients received CVac therapy, while the remaining 56 were randomised to receive either CVac or observational standard of care.

CVac was found to be generally well tolerated and non-toxic, and to trigger a Mucin-1 specific T-cell response.

Prima BioMed (ASX:PRR) shares were trading unchanged at $0.035 as of around 1.30 pm on Thursday.