Primary mucinous carcinoma of the skin

KEY CLINICAL MESSAGE: Mucinous carcinoma of the skin is clinically characterized by good mobility, slow growth, a macroscopically smooth surface, no easy contact bleeding, and no internal flow on color Doppler; it is thus difficult to distinguish from benign tumors. ABSTRACT: A 58‐year‐old man presented to our clinic complaining of a right cheek induration, growing over the previous 6 months. The tumor surface was smooth, pink, did not bleed easily, and approximately 10 mm in size with good mobility. Ultrasonography revealed a well‐circumscribed hypoechoic homogenous tumor with posterior acoustic enhancement; color Doppler displayed no internal flow. Preoperative diagnosis was intradermal type nevus or dermatofibroma. An excisional biopsy was performed under local anesthesia. The biopsy specimen unexpectedly showed tumor cells with an epithelial alveolar configuration floating in a mucin lake. The tumor cells contained enlarged nuclei and formed atypical columnar epithelium, arranged in fused, honeycomb‐like glandular ducts, indicating mucinous carcinoma.