A phase II study identified the first genomic marker – mismatch repair (MMR) deficiency – to predict response to the anti-PD-1 antibody pembrolizumab. This marker predicted responses across a range of cancers.
MMR-deficient tumors had an average of 1,782 mutations, compared to 73 mutations in MMR-proficient tumors. Higher numbers of mutations were linked to better response to pembrolizumab.
The study included three groups of patients: MMR-proficient metastatic CRC (25 patients), MMR-deficient metastatic CRC (13 patients), and other MMR-deficient cancers (10 patients). All patients had progressive metastatic cancer that had worsened despite prior treatment.
Blood marker changes such as CEA levels indicating response were seen within the first few weeks of starting treatment, and patients tended to feel better almost immediately.
Presented by Dung T. Le, MD, Johns Hopkins Kimmel Cancer Center, Johns Hopkins University, Baltimore, MD at ASCO 2015, Chicago, IL