Primary Melanoma of the Anus
Differential Diagnosis
Squamous Carcinoma of the Anus | Melanoma of the Anus |
May have adjacent squamous carcinoma in situ | May have adjacent junctional component |
CK5/6 and p63 virtually always positive | CK5/6 and p63 negative |
S100, HMB45 and MelanA negative | S100, HMB45 and/or MelanA positive |
Melanoma In Situ of the Anus | Extramammary Paget Disease |
Substantial proportion of atypical cells sit directly on the epidermal basement membrane | Atypical cells at all levels but frequently have at least one layer of normal cells separating them from the basement membrane |
No lumen formation or mucin positivity | Atypical cells may form lumens or be mucin positive |
CK7 and other keratins negative | CK7 and other broad spectrum antikeratins >95%+ |
HMB45 and MelanA 60-95%+ | HMB45 and MelanA negative |