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Ann Oncol. 2019 Aug 1;30(8):1232-1243. doi: 10.1093/annonc/mdz116.

ESMO recommendations on microsatellite instability testing for immunotherapy in cancer, and its relationship with PD-1/PD-L1 expression and tumour mutational burden: a systematic review-based approach.

Author information

Department of Diagnostics and Public Health, University of Verona, Verona, Italy.
Department of Pathology, Caen University Hospital, Caen, France.
Departments of Human Genetics Radboud university medical center, Nijmegen, The Netherlands.
Departments of Pathology, Radboud university medical center, Nijmegen, The Netherlands.
Department of Cellular Pathology, Barts Health NHS Trust, London, UK.
Department of Surgery, San Bortolo Hospital, Vicenza, Italy.
Department of Pathology, Leiden University Medical Centre, Leiden, The Netherlands.
Department of Oncology, University College London, London, UK.
Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, USA.
European Society for Medical Oncology, Lugano, Switzerland.
Department of Medical Oncology, Institut Gustave Roussy, Villejuif, France.
ARC-Net Research Centre, University of Verona, Verona, Italy.



Cancers with a defective DNA mismatch repair (dMMR) system contain thousands of mutations most frequently located in monomorphic microsatellites and are thereby defined as having microsatellite instability (MSI). Therefore, MSI is a marker of dMMR. MSI/dMMR can be identified using immunohistochemistry to detect loss of MMR proteins and/or molecular tests to show microsatellite alterations. Together with tumour mutational burden (TMB) and PD-1/PD-L1 expression, it plays a role as a predictive biomarker for immunotherapy.


To define best practices to implement the detection of dMMR tumours in clinical practice, the ESMO Translational Research and Precision Medicine Working Group launched a collaborative project, based on a systematic review-approach, to generate consensus recommendations on the: (i) definitions related to the concept of MSI/dMMR; (ii) methods of MSI/dMMR testing and (iii) relationships between MSI, TMB and PD-1/PD-L1 expression.


The MSI-related definitions, for which a consensus frame-work was used to establish definitions, included: 'microsatellites', 'MSI', 'DNA mismatch repair' and 'features of MSI tumour'. This consensus also provides recommendations on MSI testing; immunohistochemistry for the mismatch repair proteins MLH1, MSH2, MSH6 and PMS2 represents the first action to assess MSI/dMMR (consensus with strong agreement); the second method of MSI/dMMR testing is represented by polymerase chain reaction (PCR)-based assessment of microsatellite alterations using five microsatellite markers including at least BAT-25 and BAT-26 (strong agreement). Next-generation sequencing, coupling MSI and TMB analysis, may represent a decisive tool for selecting patients for immunotherapy, for common or rare cancers not belonging to the spectrum of Lynch syndrome (very strong agreement). The relationships between MSI, TMB and PD-1/PD-L1 expression are complex, and differ according to tumour types.


This ESMO initiative is a response to the urgent questions raised by the growing success of immunotherapy and provides also important insights on the relationships between MSI, TMB and PD-1/PD-L1.


immunotherapy; microsatellite instability (MSI); next-generation sequencing (NGS); tumour mutational burden (TMB); tumour mutational load (TML)


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