Biopsy of a persistent exophytic area on the vulva of a 60 year old woman demonstrates a squamous epithelial lesion. No koilocytes are seen. The lesions show papillary projections composed of disordered, squamous epithelium with well differentiated cells. The basement membrane at the dermal-epidermal junction is focally disrupted by squamous cell groups extending deep into the dermis. Which of the following diagnoses is most accurate?