MIB-1 immunostaining is a beneficial adjunct test for accurate diagnosis of vulvar condyloma acuminatum.

The histopathologic diagnosis of vulvar condyloma acuminatum is often based on architectural features that are not specific for human papillomavirus (HPV) infection. Because HPV-associated lesions show increased cellular proliferation, the authors evaluated the usefulness of MIB-1 immunostaining as an aid in the differential diagnosis of cases equivocal for condyloma. The MIB-1 immunostaining pattern was correlated with HPV DNA detection in condyloma acuminatum (CON-A; n = 15), "consistent with condyloma" (c/w CON-A; n = 26), fibroepithelial polyp (FEP; n = 14), and squamous papilloma (n = 10). HPV was detected in 100% of the CON-A cases, and all cases demonstrated MIB-1-positive nuclei in the upper two thirds of the epithelial thickness. With this definition of MIB-1 positivity, there was complete concordance between MIB-1 positivity and HPV detection for all cases (kappa = 0.88). Of the cases c/w CON-A, 17 of 26 (65%) were positive for both MIB-1 and HPV, and could be reclassified as CON-A, whereas 35% were identified as an overdiagnosis based on negative results. In addition, two cases of FEP were MIB-1 and HPV positive, and thus were identified as an underdiagnosis. These results suggest significant overdiagnosis of cases equivocal for condyloma, and indicate that MIB-1 immunostaining is a beneficial adjunctive test when the morphologic features are suggestive but not diagnostic for CON-A.