Expression of PAM4 biomarker, MUC1, MUC4, CEACAM5/6, and CA19-9 in a representative case of benign serous cystadenoma (SCA). (A) The hematoxylin-eosin section shows a multilocular cyst lined with cuboidal epithelial cells. This is the only case, of 15 cases, where (B) MAb- PAM4 and (D) MUC4 showed a diffuse, weak labeling (arrows). (C) MUC1 labeling appeared to be significantly greater than the PAM4 biomarker and MUC4, with (E) CEACAM5/6 showing little to no expression in these benign lesions, and (F) CA19-9 showing mostly weak labeling of the cyst linings (original magnifications ×40).