Subungual Squamous Cell Carcinoma of the Finger

5Department of Surgery, Orthopedic Service, Brooke Army Medical Center, San Antonio, TX 78234. 53-year-old woman presented to a dermatologist with a subungual mass in the right index finger. Radiographs revealed a subungual soft-tissue mass that had eroded into the distal phalanx of the index finger. The dermatologist performed a biopsy, revealing the diagnosis of squamous cell carcinoma. The index finger was amputated. The differential diagnosis of an erosive lesion in the distal phalanx includes implantation dermoid cyst, subungual fibroma, glomus tumor, giant cell tumor of tendon sheath, subungual squamous cell carcinoma, subungual keratoacanthoma, and mucous cyst [1]. Radiologically, subungual squamous cell carcinoma is almost indistinguishable from subungual keratoacanthoma. Keratoacanthoma is a localized endoexophytic growth of squamous epithelium with a characteristic central keratin-filled crater. Keratoacanthomas may be locally destructive and sometimes are associated with transformation to squamous cell carcinoma with subsequent invasion. Some authors consider keratoacanthoma a subset of squamous cell carcinoma [2]; however, keratoacanthomas more frequently undergo spontaneous involution, and the larger consensus is that they are separate lesions with distinctive behavior. The treatment of subungual keratoacanthoma is conservative, while that of subungual squamous cell carcinoma is amputation. Both subungual keratoacanthoma and squamous cell carcinoma may present with pain, localized swelling, and inflammation. Patients with subungual squamous cell carcinoma tend to be older (seventh decade peak) than those with keratoacanthoma (fifth decade peak) [1–4]. Squamous cell carcinoma grows slowly and often is mistaken for chronic inflammation. In contrast, subungual keratoacanthoma grows rapidly, proliferating to an obvious 1to 2-cm mass within several weeks to months; then generally stabilizes and later spontaneously involutes, leaving a small pitted scar [1]. Eighty-four percent of subungual squamous cell carcinomas occur in the fingers, the remaining in the toes. The majority of subungual squamous cell carcinoma in the fingers occurs in the thumb (44%); and those in the toes affect the great toe predominately (64%) [3, 4]. Predisposing factors for subungual squamous cell carcinoma include chronic paronychia, trauma, congenital ectodermal dysplasia, radiation exposure, and previous human papillomavirus (HPV) infection [3, 4]. In A