Somatic mutations in genes associated with mismatch repair predict survival in patients with metastatic cancer receiving immune checkpoint inhibitors

Case report: Immunotherapy guided by molecular profiling of tumors: illustrative cases and literature review

Predictive biomarkers are necessary for the identification of immunotherapy-responsive patients. Tumor mutation burden (TMB), as determined by next-generation sequencing (NGS), and PD-L1 expression, as evaluated by Immunohistochemistry (IHC), are the biomarkers most frequently employed in clinical practice. In addition, microsatellite instability (MSI) was the first biomarker to demonstrate immunotherapy efficacy irrespective of the type of tumor and possesses a high predictive value. However, its limited use across most tumor types limits its therapeutic potential. This report describes two cancer patients with positive TMB and PD-L1 expression. The molecular profile of the tumor indicated that the first patient was responsive to Immune checkpoint inhibitors (ICI), while the second patient was resistant. These case studies demonstrate that tumor molecular analysis in combination with immunotherapy predictive biomarkers, such as PD-L1 expression and TMB, can enhance the prediction of response to ICI for specific patients. This methodology enables an individualized and improved approach to the treatment and management of the disease.

A rare case of sporadic mismatch repair deficient pancreatic ductal adenocarcinoma that responded to ipilimumab and nivolumab combination treatment: case report

Background

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignant disease with a poor prognosis. Despite high efficacy in multiple cancers, immunotherapy has had very little success in treating PDAC due to unfavorable characteristics such as low tumor mutational burden (TMB), low microsatellite instability (MSI), and non-immunogenic tumor microenvironment. Recently, however, there have been reports of rare PDAC cases with high TMB and DNA mismatch repair deficiency (dMMR) that have demonstrated positive response to immunotherapy. All these cases have also presented with Lynch Syndrome, or germline mutations in MMR genes.

Case Description

Here, we report a 57-year-old male with stage IV PDAC whose tumor profile revealed high TMB, high MSI, and dMMR, but no germline mutations in genes associated with hereditary cancers including those associated with Lynch Syndrome. After a series of ineffective treatments, the patient showed positive response to combined ipilimumab and nivolumab immunotherapy. To our knowledge, this is the first report of an advanced PDAC case with sporadic dMMR, high TMB, and no Lynch Syndrome having a good response to immunotherapy.

Conclusions

This case further supports TMB and high MSI/dMMR being possible biomarkers for immunotherapy of PDAC as well as highlights the importance of both germline and somatic testing of patients with PDAC.

Incidence, clinicopathologic, and genetic characteristics of mismatch repair gene-mutated glioblastomas

BACKGROUND

Glioblastoma (GBM) is the most common and malignant gliomas of adults and recur, resulting in death, despite surgery, radiotherapy, and temozolomide-based chemotherapy. There are a few reports on immunotherapy for the mismatch repair (MMR)-deficient GBMs with high tumor mutational burden (TMB). However, the clinicopathological and genetic features of the MMR genes altered in GBMs have not been elucidated yet.

METHODS

The authors analyzed targeted next-generation sequencing (NGS) data from 282 (276 primary and 6 recurrent) glioblastomas to evaluate the mutational status of six DNA repair-related genes: MLH1, MSH2, MSH6, PMS2, POLE, and POLD1. Tumors harboring somatic or germline mutations in one or more of these six genes were classified as an MMR gene-altered GBM. The clinicopathologic and molecular characteristics of MMR gene-altered GBMs were compared to those of tumors without MMR gene alterations.

RESULTS

Sixty germline or somatic mutations were identified in 37 cases (35 primary and two recurrent) of GBM. The most frequently mutated genes were MSH6 and POLE. Single nucleotide variants were the most common, followed by frameshift deletions or insertions and approximately 60% of the mutations were germline mutations. Two patients who showed MSH2 (c.2038C > T) and MSH6 (c.1082G > A) mutations had familial colon cancer. The clinical findings were not different between the two groups. However, the presence of MGMT promoter methylation and high tumor mutation burden (TMB) values (> 20) were correlated with MMR gene alterations.

CONCLUSION

Since MMR-related genes can be found even in primary glioblastoma and are correlated with high TMB and MGMT promoter methylation, MMR genes should be carefully analyzed in NGS study on glioblastomas.