Primary retroperitoneal mucinous cystadenomas with gastric epithelial differentiation.

We present two rare cases of retroperitoneal mucinous cystadenomas (RMC) by clinical data, light microscopy, electron microscopy, histochemistry, and immunohistochemistry. Both tumors occurred in women. We excluded attachment to any organ. Additional immunohistochemical examinations were performed for comparison in 10 cases of ovarian mucinous cystadenomas (OMC). Both RMC showed no significant immunohistochemical differences from the OMC. Ultrastructurally and histologically the RMC resemble OMC reported in the literature. Immunohistologically, we proved gastric epithelial differentiation by using one monoclonal antibody (2B5) recognizing gastric mucin and one polyclonal antibody against pepsinogen II (PG II). In spite of this, the histogenesis of RMC in the presented cases in the end remains uncertain.