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Idylla MSI test as a new tool for microsatellite instability detection in sebaceous tumours and keratoacanthomas
  1. Loëtitia Favre1,2,
  2. Ruiqian Chen2,
  3. Yaëlle Bellahsen-Harrar2,
  4. Nicolas Ortonne1,2,
  5. Anaïs Pujals1,2
  1. 1 Université Paris-Est Créteil Val de Marne Faculté de médecine, Creteil, France
  2. 2 Department of Pathology, CHU Henri Mondor, Creteil, France
  1. Correspondence to Dr Loëtitia Favre, Pathology, Hôpital Henri Mondor, Creteil 94000, France; loetitia.favre{at}


Aim Sebaceous tumours and keratoacanthomas can be associated with mismatch repair (MMR) deficiency and thus microsatellite instability (MSI). In such tumours, MSI phenotype could be an argument to search for an underlying Muir-Torre syndrome (MTS). MTS has been recognised as a variant of Lynch syndrome, characterised by a deficiency of the MMR proteins. In Lynch syndrome, the sensitivity and specificity of the techniques used to detect MSI is well described, which is not the case for skin tumours. In our hands, immunohistochemistry is a sensitive and specific method to detect MMR deficiency in those tumours. Contrasting with tumours of Lynch spectrum, sensitivity and specificity of molecular methods has not been extensively studied. This study aimed at evaluating two molecular methods to detect MSI phenotype in MTS associated tumours: a commonly used pentaplex PCR using Bethesda markers and the fully automated method using the Idylla MSI assay.

Methods A comparison between PCR, and Idylla was performed on 39 DNA extracted from cutaneous tumours. Immunohistochemistry was used as the gold standard to calculate sensitivity and specificity of both molecular techniques.

Results Concordant results were found in 32 cases (82%) with pentaplex PCR and in 36 cases (92%) with Idylla. The sensitivity of pentaplex PCR to detect MSI phenotype was 76% whereas Idylla sensitivity was 90%.

Conclusion Idylla is more performant than PCR, for the detection of MSI in MTS-associated tumours and is a reliable additional technique to help detecting MTS in these tumours.

  • medical oncology
  • carcinoma
  • skin neoplasms
  • pathology
  • molecular

Data availability statement

All data relevant to the study are included in the article.

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Data availability statement

All data relevant to the study are included in the article.

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  • Handling editor Runjan Chetty.

  • LF and RC contributed equally.

  • NO and AP contributed equally.

  • Contributors RC and LF performed experiments and analysed the data; RC, LF and YB-H wrote draft manuscript. NO and RC reviewed the slides. AP secured funding and designed the experiment. NO and AP reviewed the manuscript. NO and AP are the guarantor of this work and, as such, had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.