Histologic Variants of Squamous Cell Carcinoma of the Skin

Margaret H. Rinker, MD; Neil A. Fenske, MD; Leigh Ann Scalf, MD, and L. Frank Glass, MD, Division of Dermatology and Cutaneous Surgery, Department of Internal Medicine at the University of South Florida, Tampa, Fla.

Cancer Control. 2001;8(4) 

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Epithelioma Cuniculatum

Epithelioma cuniculatum, also referred to as carcinoma cuniculatum,was first described by Aird et al in 1954.[21] The word epitheliomameans "tumor of the epithelium"and cuniculate refers to crypt-like spaces seen on histology that resemble rabbit burrows. Since its original description,more than 100 cases have been reported with this variant of SCC. It is now thought to represent a variant of verrucous carcinoma localized to the plantar surface. Trauma, chronic irritation,and HPV infection have been implicated as possible triggering factors.[24]

Epithelioma cuniculatum is often seen in older white men. The mean age of presentation is 52-60 years, with a range of 23-84 years.[25] It tends to occur most commonly on the ball of the sole (53%), followed by the toes (21%) and the heel (16%).[24] Initially, the tumor may resemble a plantar wart, but it may slowly progress to form a bulky, exophytic mass. It may become ulcerated and develop numerous sinuses from which afoul-smelling purulent keratinous debris can be expressed. It has often been described as a "squashy"mass, with the consistency of an overripe orange.[25] The tumor can be deforming and painful, leading to difficulty with ambulation.

On histology, it has both an endophytic and exophytic growth pattern. The cells are well differentiated,and pronounced hyperkeratosis and papillomatosis are usually present. Tumor strands may extend deep into the dermis and sub cutis,forming keratin-filled intraepidermal abscesses and sinuses with the surface. These sinus tracts are the"rabbit-burrow-like spaces" from which epithelioma cuniculatum derives its name. The surrounding stroma may demonstrate an infiltrate of lymphocytes, histiocytes,eosinophils, and plasma cells. On close examination, atypia with nuclear enlargement, hyperchromasia,and mitoses may be evident.[24] The major differential diagnoses include pseudoepitheliomatous hyperplasia and giant plantar warts.

Although it is not considered an aggressive form of SCC, there have been reports of metastases to skin and lymph nodes. In a study of 46 cases by Kao and colleagues,[24] follow-up data were obtained on [26] patients. Three patients had local recurrence and three had distant metastases. None of the patients at that time had disseminated disease or died of metastatic disease.

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