MUC3A and adenocarcinoma: Depending on the presence/absence of mucins, adenocarcinomas have been classified as having a gastric (i.e., tumors expressing only gastric MUC1, MUC5AC, and/or MUC6 mucins), intestinal (i.e., tumors expressing only intestinal MUC2, MUC3, MUC4, and/or MUC13 mucins), mixed (i.e., tumors expressing both gastric and intestinal mucins), or unclassified/null (i.e., tumors expressing nor gastric, nor intestinal mucins) mucin phenotype [9–15].