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Jun Gong, Chongkai Wang, Peter P. Lee, Peiguo Chu and Marwan Fakih

Recent clinical evidence has demonstrated that microsatellite instability (MSI) or defective mismatch repair (MMR) and high tumor mutational load can predict response to the programmed cell death 1 (PD-1) receptor inhibitor pembrolizumab in metastatic colorectal cancer (mCRC). Mutations in polymerase ε (POLE), a DNA polymerase involved in DNA replication and repair, contribute to an ultramutated but microsatellite stable (MSS) phenotype in colorectal tumors that is uniquely distinct from MSI tumors. This report presents the first case in the literature describing a clinical response to pembrolizumab in an 81-year-old man with treatment-refractory mCRC characterized by an MSS phenotype and POLE mutation identified on genomic profiling by next-generation sequencing. On tumor immunostaining, a large amount of CD8-positive tumor infiltrating lymphocytes (TILs) were present, with >90% of these expressing PD-1. More than 99% of PD-L1 expression was identified on nontumor cells in the tumor microenvironment that were close to the PD-1–positive CD8 TILs. mCRC tumors harboring POLE mutations represent a hypermutated phenotype that may predict response to anti–PD-1 therapy.

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Justin A. Chen, Naseem Esteghamat, Edward J. Kim, Gabriel Garcia, Jun Gong, Marwan G. Fakih, Richard J. Bold and May T. Cho

Immune checkpoint inhibitors represent a newly established standard of care in patients with refractory metastatic colorectal cancer with mismatch repair deficiency and microsatellite instability. However, the use of immunotherapy is unclear in recipients of liver transplants with or without concurrent liver function abnormalities. Clinical trials investigating immunotherapy have mostly excluded liver transplant recipients and patients with abnormal liver function. This report presents the first case, to our knowledge, of a liver transplant patient with mismatch repair–deficient colon adenocarcinoma with liver metastases and concurrent abnormal liver function who safely responded to immunotherapy. We also review the literature on checkpoint inhibitor use in patients with other metastatic solid tumors after liver transplant and those with baseline liver function abnormalities. An increasing body of evidence supports the safety of checkpoint inhibition in patients with cancer and solid organ transplants, but further prospective studies are warranted. Use of immunotherapy in liver transplant recipients who have metastatic colorectal cancer with microsatellite instability is feasible but should be performed in a multidisciplinary team setting.