The use of immunohistochemistry in detection of perineural invasion in mucoepidermoid carcinoma.

Objectives To retrospectively study the prevalence of perineural invasion (PNI) in cases of mucoepidermoid carcinoma (MEC). The study evaluated if previously assessed PNI would be increased by re-review of the original hematoxylin and eosin–stained (H&E) slides and also review of slides reacted immunohistochemically with S100 to enhance nerve visualization and whether this is associated with clinical outcome. Study Design Thirty-one cases were reviewed for PNI with H&E-stained slides as well as S-100-reacted slides. These results were compared with the original pathology report's PNI status when available (13 of 31). Subject demographic characteristics and clinical outcome were collected from electronic medical records. Results PNI was identified in 23% (3 of 13) of tumors in the original reports, 13% (4 of 31) of the authors' re-review of the slides, and 29% (9 of 31) by immunohistochemical assessment for S100. PNI and larger-diameter nerve involvement were significantly associated with death at 5-year follow-up. Conclusions Immunohistochemical assessment for S100 improves the accuracy of PNI determination. PNI is a significant factor in the survival outcome of cases of MEC.