Eosinophils as a marker for invasion in vulvar squamous neoplastic lesions

A study of eosinophils directed against vulvar neoplastic squamous epithelium was undertaken to determine whether there were thresholds per high-power field (hpf) or 10 hpf that were a marker for invasion. The presence of stromal and intraepithelial eosinophils in 33 cases of vulvar grade 3 squamous intraepithelial neoplasia (carcinoma in situ) (VIN 3) was compared with that in 38 cases of vulvar invasive carcinoma with any degree of invasion (ISC). In both incisional biopsy and excisional specimens, the presence of >3 eosinophils per high-power field (eos/hpf) and the presence of >or=5 eosinophils per 10 high-power fields (eos/10 hpf) were both significantly associated with invasion, and the presence of >or=20 eos/hpf and/or >50 eos/10 hpf was limited to cases with invasion. The presence of eosinophils within the neoplastic squamous epithelium was also limited to cases with invasion. The author proposes: 1) eosinophil counts in vulvar incisional biopsy specimens of >3/hpf and/or >or=5/10 hpf warrant a note of caution that invasion may be present even when none is identified by conventional criteria; 2) eosinophil counts of >3/hpf and/or >or=5/10 hpf in excisional specimens should raise the suspicion of invasion in cases in which only VIN 3 is identified in the initial sections, and warrant additional sections and/or levels to search for invasion; 3) the above eosinophil counts provide supportive evidence for invasion in cases with equivocal invasion by conventional criteria; and 4) the presence of >or=20 eos/hpf and/or >50 eos/10 hpf, and the presence of intraepithelial eosinophils in conjunction with >3 eos/hpf and >or=5 eos/10 hpf is virtually diagnostic of invasion.