A new College of American Pathologists (CAP) evidence-based guideline is among the first to address testing based less on the cancer type or tumour origin and more on the methodology and status of a biomarker.
The Mismatch Repair (MMR) and Microsatellite Instability (MSI) Testing for Immune Checkpoint Inhibitor Therapy guideline provides clarity for pathologists and oncologists to improve the evaluation of patients with colorectal (pictured), endometrial, gastroesophageal, small bowel, and certain other cancers who may be eligible for immunotherapies known as immune checkpoint inhibitors.
Published recently in an early online release in the journal Archives of Pathology & Laboratory Medicine, the guideline (access the guideline here) also breaks new ground with recommendations on the role of tumour mutational burden in MMR testing and the evaluation for Lynch syndrome, a hereditary cancer syndrome that may be unexpectedly detected in the work-up of these patients with advanced cancers. The CAP developed the guideline in collaboration with experts from the Association for Molecular Pathology (AMP), the American Society of Clinical Oncology (ASCO), and the patient advocacy group Fight Colorectal Cancer (Fight CRC).
“We’ve seen that patients whose cancers had high levels of MSI or defective MMR can respond well to immune checkpoint inhibitor therapy, and now we have objective guidance to assess that status across a range of cancer types,” explained pathologist Dr Russell Broaddus, who led the expert panel to develop the guideline.
Dr Broaddus noted that when the FDA-approved immunotherapy treatment for patients with MSI-high or MMR-deficient tumour status, regardless of cancer type, it did not detail how to test for that status. The new CAP guideline helps to fill that gap, providing oncologists, pathologists, and laboratories of all sizes with objective, evidence-based recommendations to efficiently deploy specific assays and accurately identify patients eligible for treatment.
With six recommendations and three good practice statements, the guideline provides data and details regarding the efficacy and utility of specific testing modalities across applicable cancer types, including MMR by immunohistochemistry, MSI by polymerase chain reaction, and MSI by next-generation sequencing, for patients being treated with immune checkpoint inhibitors. In addition, the guideline identifies gaps in our current knowledge base, which, when addressed, may represent opportunities to help improve the methodological approach for identifying the patients with advanced cancers who are most likely to respond to this therapeutic approach.
