REG4 and mucinous cystadenoma: Immunostaining revealed that REG4 was strongly expressed in the cytoplasm of serous and mucinous adenoma, serous and mucinous borderline tumors, serous and mucinous adenocarcinoma, and adenocarcinoma in the omentum; but was not expressed in the fiber cells of normal ovarian tissue and only very weakly in the fallopian tube (Fig. 5).