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Expert Discusses Phase III Trial of Frontline Pembrolizumab in MSI-H Colorectal Cancer

Danielle Bucco
Published: Friday, Jun 30, 2017

Luis A. Diaz, MD

Luis A. Diaz, MD

Pembrolizumab (Keytruda) has demonstrated antitumor activity in heavily pretreated patients with microsatellite instability-high (MSI-H) colorectal cancer (CRC). Now, in the phase III KEYNOTE-177 trial, investigators hope to show that frontline treatment with the PD-1 inhibitor can improve progression-free survival (PFS) compared with standard-of-care chemotherapy.

conducted at the 2017 ASCO Annual Meeting, Diaz, head of the division of Solid Tumor Oncology at Memorial Sloan Kettering Cancer Center, discussed KEYNOTE-177 and the implications of the FDA approval of pembrolizumab for patients with MSI-H or dMMR CRC or other solid tumors.

OncLive: What where you hoping to find when you began studying pembrolizumab?

Diaz: When we started the study, we didn't know if it would be limited to CRC or to other tumors. We thought it would be something that we would see across many different tumor types. What was remarkable was we discovered that not only did colon cancers respond excellently, but also endometrial cancers, gastric cancers, small intestine cancers, pancreatic cancers, brain tumors, prostate cancers, and more, as we kept adding patients who are mismatch deficient across any tumor type and we started seeing responses. The thinking has started to change—perhaps this is a genetic alteration that is a more powerful indicator than where the tumor comes from.

Even in the original study that we started in 2012 and reported in 2015, we still have not reached the median OS. These patients are doing extraordinarily well. I think the approval is well warranted and the data is exciting.

As you said, the sample size in CRC was tiny. Why do you think the FDA was so impressed?

The main data here is showing that in CRC and non-CRC, we're seeing response rates with pembrolizumab that are quite impressive. The PFS and OS are quite durable, and it's recapitulated in entirely different studies. I believe that is what led to the FDA approval.
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