Utility of mismatch repair protein expression screening via an endoscopic ultrasound assessment of treatment-naive pancreas ductal adenocarcinoma.

We read with great interest the recent articles by Luchini et al 1 2 and Grant et al 3 highlighting the low prevalence (1%–2%) of mismatch repair deficient pancreatic ductal adenocarcinoma (dMMR PDAC) and offering further knowledge pertaining to the molecular spectrum of this disease subtype. A plea was raised to augment translational and clinical research efforts to improve our understanding of dMMR PDAC. However, from a practical perspective, only 20% of patients with PDAC reach surgical oncologic resection.4 These resection specimens have served as the source of prior dMMR PDAC analysis. Following the United States Food and Drug Administration approval of pembrolizumab as the first cancer therapy targeting a specific molecular signature, we identified a dMMR prevalence of 3% in a small retrospective cohort of archived pancreas endoscopic ultrasound fine-needle biopsy (EUS FNB) specimens.5 We recently completed an 18-month prospective evaluation of 218 consecutive treatment-naive PDAC patients diagnosed by EUS (fine-needle aspiration: 112 (51.4%), FNB: 91 (41.7%) or both: 15 (6.9%)) for MMR screening as a companion diagnostic test (table 1). A specimen adequate for ancillary studies was acquired in 193 (88.5%) patients …