Carcinoma Cuniculatum of the Hand: A Case Report.

INTRODUCTION: Cutaneous squamous cell carcinoma (cSCC) is a common malignant skin cancer arising from epidermal squamous cells, typically developing on chronically sun-exposed skin. The clinical diagnosis of cSCC is usually rather straightforward, although one should be aware of rare and atypical subtypes. CASE PRESENTATION: An 83-year-old woman, hospitalized for the workup of auricular fibrillation, presented a 10 × 5.5 cm, indolent, indurated, slightly purulent, tumoral mass on her left hand, that progressively increased in volume since around 2 years. There was no functional failure and no locoregional adenopathies. The first punch biopsy favored a keratoacanthoma. The culture of the purulent discharge revealed no microorganisms. MRI did not reveal any deep soft tissue or bone invasion. Excisional surgery was performed under local anesthesia. Histology revealed a well-differentiated cSCC-like exophytic tumor with an endophytic architecture composed of tortuous, keratin-filled, interconnected crypts, highly suggestive of cSCC of the cuniculatum type. CONCLUSION: Carcinoma cuniculatum is an exceptional subtype of cSCC, with an indolent clinical evolution and a well-differentiated histological presentation. Dermatologists and plastic surgeons should be aware of this rare type of cSCC that is to be differentiated from verrucous carcinoma, keratoacanthoma, cSCC and pseudo-epitheliomatous hyperplasia. Aggressive therapy must be avoided as deep invasion is exceptional, the growth is highly indolent and locoregional or systemic metastatic lesions are nearly never observed. Surgical excision is the cornerstone of treatment.