The objective of this study was to retrospectively evaluate the prevalence of perineural invasion in cases of mucoepidermoid carcinoma (MEC). The study will determine if previously assessed perineural invasion by original pathology reports would be increased by re-review of the originally hematoxylin-eosin-(H&E) stained slides as well as review of slides reacted immunohistochemically with S100 to enhance visualization of nerves. The study will also assess whether perineural invasion or its absence in MEC is associated with clinical outcome. Thirty-one cases of major and minor salivary gland MEC were reviewed for perineural invasion and compared to the perineural invasion status stated on the original pathology report when available (13/31). All H&E slides were reviewed as well as S100-reacted sections of each case's tissue blocks that contained tumor. Patient demographics and clinical outcome were collected from electronic medical records. Perineural invasion was identified in 23% (3/13) of tumors in the original reports, 13% (4/31) of the authors' re-review of the same slides, and 29% (9/31) when cases were reacted with S100. A positive relationship was seen between the discovery of perineural invasion on H&E slides and a greater number of foci of perineural invasion. Perineural invasion and larger-diameter nerve involvement was significantly associated with death at 5-year follow-up. In conclusion, immunohistochemical enhancement improves the accuracy, ease and speed of perineural invasion determination. Perineural invasion is a significant factor in the decreased survival outcome of cases of MEC. These findings support continued inclusion of the presence or absence of perineural invasion as a grading parameter in MEC.
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