16% of the time, it works every time.

A new study in JCO describes impressive durable disease control in metastatic melanoma patients who have complete responses (CR) to pembrolizumab. This data comes from the original KEYNOTE-001 trial of pembro for patients with metastatic melanoma. The overall CR rate was only 16%, but 90%(!) of these patients remained disease-free at two years. An important takeaway is the timing of response: while half of patients showed some response within 3 months, the median time to CR was over 1 year. Remarkably, the majority of patients (>80%) discontinued pembro after CR, translating to a median of 22 months off therapy. Predictors of durable response? Older age, PD-L1 expression, and smaller tumor burden (<5 cm). This last point brings up an interesting question of whether cytoreductive SBRT or surgery could potentially improve upon these meager rates of mighty responses.