A Case of an Undifferentiated Squamous Cell Carcinoma Arising from an Epidermal Cyst

An epidermal cyst is a common benign subcutaneous tumor and rarely develops malignancy. We report a case of an undifferentiated cutaneous squamous cell carcinoma (SCC) that arose from an epidermal cyst on the left side of the neck. The epidermal cyst had rapidly increased in size and presented cauliflower-like tumor. Histological study revealed undifferentiated squamous cell carcinoma that was arising from the epidermal cyst. 1. Introduction An epidermal cyst is a common benign subcutaneous tumor and rarely develops malignancy. We report a case of an undifferentiated cutaneous squamous cell carcinoma (SCC) that arose from an epidermal cyst on the left side of the neck. 2. Case Presentation A 65-year-old man presented with a cauliflower-like tumor from a cyst on the left side of the neck (Figure 1). He reported that the cyst had existed for 35 years and had received occasional puncture. The cyst had gradually begun to increase in size and discharged bloody fluid 6 months prior to his hospital visit. The result of an excision biopsy from the tumor was not decisive because of the abundant hemorrhage and inflammation in the specimen. Magnetic resonance imaging and computed tomography (CT) revealed that although the tumor was 9？cm in diameter, it was completely encapsulated by the wall of the cyst and free of tumor invasion. Enhanced CT and 18F-FDG positron emission tomography (PET) showed neither distant metastasis nor lymph node metastasis. We suspected that the tumor was a SCC arising from an epidermal cyst. Figure 1: Most part of the tumor was confined into the epidermal cyst although cauliflower-like excrescence was observed from the fissure. (a) Anterior side. (b) Posterior side. A surgical excision of the tumor with 1？cm margin was performed. The pathological examination was consistent with an undifferentiated SCC arising from an epidermal cyst (Figures 2 and 3). There was no sign of specific differentiation such as ductal formation or keratinization. Immunological staining showed that CAM5.2, vimentin, and EMA were positive while pankeratin, CK5, CK34βE12, S100, melan A, desmin, αSMA, and myogenin were negative. Therefore, we diagnosed a primary cutaneous SCC. Figure 2: The squamous cell carcinoma developed within the epidermal cyst. (H and E ). Figure 3: The tumor cells had eosinophilic cytoplasm and distinctive nucleoli that showed mitosis in some parts. (H and E ). As the surgical margin was negative but close to the bottom of the cyst, postoperative radiation therapy is additionally planned. 3. Discussion Reported rates of SCC arising from