Unusual skin mass (primary cutaneous mucinous carcinoma).

Primary mucinous carcinoma of the skin is a rare malignant tumour of sweat gland origin. Diagnostic concerns include its deceptively benign appearance in some cases and the difficulty in differentiating it from secondary mucinous carcinoma of skin metastasising from a primary source elsewhere. A case of a 75-year-old man is reported who presented with a slowly growing painless mass near the lateral canthus of the right eye for about 2 years. Clinically, a diagnosis of basal cell carcinoma was made whereas histopathology revealed mucinous carcinoma of the skin. The primary source of the tumour could not be found on detailed physical examination and laboratory investigations. Immunohistochemistry, performed later, was consistent with primary cutaneous mucinous carcinoma.