Tumor mutational burden is predictive of response to immune checkpoint inhibitors in MSI-high metastatic colorectal cancer

Ann Oncol. 2019 Jul 1;30(7):1096-1103. doi: 10.1093/annonc/mdz134.


Background: Microsatellite instability (MSI) is a biomarker for response to immune checkpoint inhibitors (ICPIs). PD-1 inhibitors in metastatic colorectal carcinoma (mCRC) with MSI-high (MSI-H) have demonstrated a high disease control rate and favorable progression-free survival (PFS); however, reported response rates to pembrolizumab and nivolumab are variable and often <50%, suggesting that additional predictive biomarkers are needed.

Methods: Clinicopathologic data were collected from patients with MSI-H mCRC confirmed by hybrid capture-based next-generation sequencing (NGS) treated with PD-1/L1 inhibitors at five institutes. Tumor mutational burden (TMB) was determined on 0.8-1.1 Mb of sequenced DNA and reported as mutations/Mb. Potential biomarkers of response and time to progression were analyzed by univariate and multivariate analyses. Once TMB was confirmed as a predictive biomarker, a larger dataset of 18 140 unique CRC patients was analyzed to define the relevance of the identified TMB cut-point.

Results: A total of 22 patients were treated with PD-1/L1 inhibitors including 19 with pembrolizumab monotherapy. Among tested variables, TMB showed the strongest association with objective response (OR; P < 0.001) and PFS, by univariate (P < 0.001) and multivariate analysis (P < 0.01). Using log-rank statistics, the optimal predictive cut-point for TMB was estimated between 37 and 41 mutations/Mb. All 13 TMBhigh cases responded, while 6/9 TMBlow cases had progressive disease. The median PFS for TMBhigh has not been reached (median follow-up >18 months) while the median PFS for TMBlow was 2 months. A TMB of 37.4 mutations/Mb in a large MSI-H mCRC population (821/18, 140 cases; 4.5%) evaluated by NGS corresponded to the 35th percentile cut-point.

Conclusions: TMB appears to be an important independent biomarker within MSI-H mCRC to stratify patients for likelihood of response to ICPIs. If validated in prospective studies, TMB may play an important role in guiding the sequencing and/or combinations of ICPIs in MSI-H mCRC.

Keywords: checkpoint inhibitor; colorectal cancer (CRC); immunotherapy; microsatellite instability (MSI); tumor mutational burden (TMB).

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Monoclonal, Humanized / administration & dosage
  • Antineoplastic Combined Chemotherapy Protocols / therapeutic use*
  • B7-H1 Antigen / antagonists & inhibitors
  • Biomarkers, Tumor / genetics
  • Colorectal Neoplasms / drug therapy*
  • Colorectal Neoplasms / genetics*
  • Colorectal Neoplasms / immunology
  • Colorectal Neoplasms / pathology
  • Female
  • Follow-Up Studies
  • Genetic Testing
  • High-Throughput Nucleotide Sequencing
  • Humans
  • Liver Neoplasms / drug therapy*
  • Liver Neoplasms / genetics
  • Liver Neoplasms / secondary*
  • Lymphatic Metastasis
  • Male
  • Microsatellite Instability
  • Middle Aged
  • Mutation*
  • Nivolumab / administration & dosage
  • Peritoneal Neoplasms / drug therapy
  • Peritoneal Neoplasms / genetics
  • Peritoneal Neoplasms / secondary*
  • Prognosis
  • Programmed Cell Death 1 Receptor / antagonists & inhibitors
  • Retrospective Studies
  • Survival Rate


  • Antibodies, Monoclonal, Humanized
  • B7-H1 Antigen
  • Biomarkers, Tumor
  • CD274 protein, human
  • PDCD1 protein, human
  • Programmed Cell Death 1 Receptor
  • Nivolumab
  • pembrolizumab