Detecting Lynch syndrome in pancreatic ductal adenocarcinoma FNA cytology based on cancer history and immunocytochemistry.

We have read with interest recent articles1–3 about microsatellite instability (MSI) in pancreatic ductal adenocarcinoma (PDAC). Although MSI is rare in PDAC, occurring in only 1%–2% of patients, it is of key importance to recognise in view of a likely better prognosis and responsiveness to immunotherapy.4 In addition, identifying MSI in a tumour may represent the initial step in the recognition of a hereditary form of cancer (Lynch syndrome (LS)), facilitating family screening and surveillance.5 Considering the rarity of MSI in PDAC, the question is how to select patients for MSI testing. Previously, it has been advised to routinely examine specific histological PDAC subtypes (ie, mucinous/colloid and medullary type) for MSI status. With this letter, we underscore the importance of cancer history as another indicator for MSI testing in PDAC. A 76-year-old patient was diagnosed with PDAC by fine needle aspiration(FNA) cytology (figure 1A). A history of cervical cancer at the age of 48 years was mentioned in the medical record, but the …