Bidirectional gastric differentiation in cellular mucin phenotype (foveolar and pyloric) in serrated adenoma and hyperplastic polyp of the colorectum

This study examined whether gastric pyloric gland‐type mucin is expressed in serrated adenoma (SA) and in hyperplastic polyp (HP) of the colorectum, and whether cellular position‐based gastric differentiation is observed in these lesions as previously hypothesized. Immunostaining was performed for MUC6 and α‐linked GlcNAc residue (pyloric gland‐type mucin markers), human gastric mucin (HGM; foveolar‐type mucin marker) and Ki‐67 (proliferating cell marker) for 31 SA, 22 HP, 21 traditional tubular adenoma (TA) and 20 hyperplastic nodule (HN). MUC6 showed varying expression in SA, 22/31 (71.0%); HP, 15/22 (68.2%); TA, 2/21 (9.5%); and HN, 0/20 (0%) with significantly higher frequencies in SA and HP compared to those in TA and HN. The α‐linked GlcNAc residue was found only in SA (3/31, 9.7%) and in HP (2/22, 9.1%). In SA and HP, HGM was typically expressed in the entire crypt length, but some reduction in expression was shown in the basal crypt portion below the proliferative zone. MUC6 and α‐linked GlcNAc residues were expressed in the basal crypt portion below or below and including proliferative zone. These data demonstrate that SA and HP show bidirectional gastric (foveolar and pyloric gland) differentiation with respect to mucin cellular phenotype and the potential for cellular position‐based differentiation, which mimics the gastric antral mucosa.