Fine needle aspiration biopsy of primary mucinous carcinoma of the skin: a case report.

Background: Primary mucinous carcinoma of the skin is a rare neoplasm of sweat gland origin. To date there are only 2 case reports in English describing its features on fine needle aspiration biopsy (FNAB). We describe an additional case and review the literature regarding this entity. To the best of our knowledge, this is the first reported case with a sentinel lymph node biopsy.

Case: A 78-year-old woman presented with a 3-cm left scalp mass at an outside institution. Following incomplete excision, multiple subcentimeter nodules developed in the skin adjacent to the biopsy site. FNAB of the nodules confirmed a recurrence of mucinous carcinoma. Clinical examination and extensive radiographic studies did not reveal primary disease elsewhere, thus supporting a diagnosis of primary mucinous carcinoma of the skin. At the time of wide excision of the residual tumor, sentinel lymph node biopsy revealed a single focus of micrometastasis. The patient declined adjuvant therapy and was disease free 6 months after the initial diagnosis.

Conclusion: Cutaneous mucinous carcinoma is a tumor characterized by bland histocytologic features and abundant extracellular pools of mucin. Without a high index of suspicion, this rare entity may be overlooked or misdiagnosed. Numerous benign and malignant mucin-producing primary and secondary mimics exist, and immunohistochemistry offers limited benefits in differentiating them. Cytologic diagnosis of primary mucinous carcinoma of the skin is possible; however, correlation of clinical, radiologic and pathologic features is necessary to arrive at an accurate diagnosis.