Abstract:

Squamous cell carcinoma (SCC) arising from an epidermal inclusion cyst (EIC) is rare, with a reported incidence between 0.011 to 0.045%. It has a predilection for head and neck region. We present a case of a 70-year-old man with a 2 cm scalp nodule with a persistent discharge. The nodule was resected based on the clinical impression of EIC. Histologic exam showed a dermal cyst with a squamous epithelial lining and keratinaceous material in the cyst lumen, consistent with an EIC. However, most of the cyst lining and the lumen was replaced by an atypical squamous cell proliferation. These atypical squamous cells were contiguous with the cyst lining, without involvement of the overlying epidermis. The cells showed nuclear pleomorphism with prominent nucleoli, moderate cytoplasm, and cytoplasmic keratin. Small focus showed poorly differentiated tumor with marked pleomorphism, large and bizarre nuclei and absence of squamous differentiation. Immunostains for pancytokeratin and p40 were positive in both moderate and poorly differentiated areas of the tumor, consistent with SCC. Focal invasion into the connective tissue was also present, however, the margins were clear. There is no evidence of recurrence in the eight months follow up postoperatively. This case is a rare example of invasive SCC arising in an EIC. We recommend histopathologic evaluation of all the surgical specimens to avoid missing an unexpected malignancy.

Financial Disclosure:
No current or relevant financial relationships exist.

Menu

Suzanne Alkul, BS, MD