Baneckova M, Michal M, Laco J, et al. - This research intended to estimate the immunohistochemical and genetic profiles of 10 cases of respiratory epithelial adenomatoid hamartoma (REAH)/seromucinous hamartoma (SH), with serous, mucinous, and respiratory components evaluated separately and to compare these findings with the features of 9 cases of low-grade tubulopapillary adenocarcinoma (LGTA). The researcher examined all cases of REAH/SH and LGTA immunohistochemically with a cocktail of mucin antigens (MUC1, MUC2, MUC4, MUC5AC, MUC6) and with epithelial (CK7, CK20, CDX2, SATB2) and myoepithelial markers (S100 protein, p63, SOX10). This study conducted next-generation sequencing assay utilizing FusionPlex Solid Tumor Kit (ArcherDx) in 10 cases of REAH/SH, and the EGFR-ZNF267 gene fusion was detected in 1 of them. Results indicated that the serous component of REAH/SH was positive for CK7/MUC1 and SOX10 similarly to LGTA. Even if REAH/SH and LGTA are histopathologically and clinically separate entities, the overlap in their morphological and immunohistochemical profiles implies that REAH/SH might be a forebear lesion of LGTA.