Esophageal submucosal gland duct adenoma: An unrecognised esophageal counterpart of minor salivary gland tumours with frequent BRAF V600E mutations.

Aims: Esophageal submucosal gland duct adenoma is an extremely rare benign tumour, with only a few reported cases. We conducted the largest single-centre clinical study of esophageal submucosal gland duct adenoma, examining its molecular mechanisms and clinicopathological features.

Methods and results: Between 2018 and 2023, seven cases of esophageal submucosal gland duct adenoma were identified at a tertiary medical centre; two were female and five were male, aged between 51 and 75 years (mean = 63.8 years). Comprehensive evaluations of clinicopathological, immunohistochemical and molecular characteristics were conducted. Histologically, tumours showed papillotubular and cystic patterns lined with double layers of cells arranged in ducts, papillary folds and microcysts. The inner luminal tall columnar cells had eosinophilic cytoplasm and did not show mucin production and the basal cells showed myoepithelial differentiation. Immunohistochemically, inner luminal  layer cells were positive for CK7, CK19 and CK5/6 and outer basal layer cells were positive for SMA and P40. Both layers were negative for CK20, CDX2, MUC5AC, MUC6, MUC2, GCDFP15 and Alcian blue-periodic acid-Schiff (AB-PAS). Genomic analyses revealed the presence of BRAF V600E mutations in five of seven tumours (71.43%).

Conclusions: This study delineates a distinct subtype of benign adenoma arising from the esophageal submucosal gland duct, characterised by multiple lobulated cystic proliferation of benign epithelial layers within the submucosa. BRAF V600E mutations were present, similar to in sialadenoma papilliferum. We determined the genetic mutation present in esophageal submucosal gland duct adenoma, providing further evidence that it is an esophageal counterpart of minor salivary gland tumours.