This is actually the largest study in the world to ever be conducted in Merkel cell carcinoma, which is a rare tumour. We wanted to test the role of immunotherapy in patients after surgical resection, so an adjuvant therapy trial using the anti-PD-1 inhibitor pembrolizumab.

What was the study design?

The study was designed to be a randomised phase III trial and the total enrolment was 293 patients, which were about equally balanced between the two arms. Our primary endpoint was relapse free survival with a secondary endpoint of overall survival. Only the relapse free survival endpoint will be presented at this conference and a secondary endpoint of distant metastasis free survival.

What did you find?

We found that patients in the arm that received pembrolizumab had a numerically but not statistically significant difference in relapse free survival compared to the patients on the standard of care arm. It’s important to note that patients on both arms were offered radiation therapy at the physician’s discretion. Essentially the bottom line is that we saw that patients who received pembrolizumab had a 81% chance of recurrence at 12 months versus 73% in patients who received the standard of care arm but this did not meet statistical significance.

What we’re very interested and excited in, however, is the data on the distant metastasis free survival endpoint. In fact, it does look like patients who received pembrolizumab had a decreased risk of spread to vital organs such as lung, lymph nodes, liver, that are outside the area of initial diagnosis. That was statistically significant with a p-value of 0.32. So what that means is that anti-PD-1 therapy does provide some protection against distant spread of the disease.

What was the safety profile?

Essentially the safety profile is very similar to what we would have expected for patients who get anti-PD-1 therapy. The toxicity that we measured was treatment related so that included radiation toxicity. The incidence of the two combined, pembrolizumab and radiation, in that arm was 31% grade 3 toxicity compared to 4% in the standard of care arm.

What are the implications of these findings?

We do need to wait for some more data, we’re going to be doing further subset analyses as well as overall survival analyses. But what it means in the meantime is that it’s certainly very possible that giving immunotherapy is a way to protect against a spread that can be a life-threatening recurrence.