Primary mucinous carcinoma of the skin

ARTICLE

Auteur(s) : Samuel Ho Yew Ming, Nallanthamby Vigneswaran, Marcus Wong Thien Chong

Section of Plastic, Reconstructive and Aesthetic Surgery, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433, Singapore

We present a 48-year-old man who initially underwent an excisional biopsy for what was thought to be an epidermal cyst on the left cheek. Eventual histology showed a circumscribed nodule of invasive mucinous carcinoma.

CT scans of the neck, PNS, salivary glands, thorax and abdomen, and a PET scan of the whole body showed no significant abnormalities. The patient declined secondary surgery and opted for surveillance. He missed subsequent appointments.

The patient presented again with a left cheek lump of increasing size at the same site 10 months later. He underwent a wide resection with 10 mm radial margins and primary closure.

Primary mucinous carcinoma of the skin (PMC) is an uncommon sweat gland tumour subtype. Since Lennox's initial description, infrequent reports have centered on the exclusion of a metastatic mucinous tumour to the skin, the difficulty with histological identification of PMC of the skin, the low rate of metastases, and the high rate of local recurrence despite best efforts at local wide resection [1, 2].

PMC has an incidence rate of 0.07 per million and usually occurs in the 7^th decade of life [3]. Common sites for PMC include the head and neck regions, with the eyelid the most common site (~41%). Less common sites include the face, scalp, axilla and trunk.

PMC is characterised by large amounts of small cord- or nest-like clusters of epithelial cells amidst pools of extracellular periodic acid-Schiff-positive, diastase-resistant mucin [4]. The importance is the exclusion of a mucin-secreting metastatic tumour to the skin. Common sites to exclude are the breast, gastrointestinal tract, salivary glands, prostate and ovaries. Histopathologically, it is difficult to differentiate between a metastatic tumour and PMC. However, immunohistochemistry would be useful. The basis is that PMC express low molecular weight cytokeratins (CK 7, CAM 5.2), carcinoembryonic antigen, epithelial membrane antigen, human milk factor globulins (HMFGI and II), gross cystic disease fluid protein, s-100 protein, alpha-lactalbumin, TFF1 (mucous-associated peptides of the trefoil factor family) and oestrogen/progesterone receptors. Other chemical characteristics that would distinguish PMC from a metastatic mucin-secreting tumour would include positive staining of the mucin with colloidal iron, periodic acid-Schiff (PAS) and mucicarmine (figure 1). Alcian blue is positive at pH 2.5 but negative at pH 0.4 or in the presence of sialidase. This histochemical profile is consistent with the presence of a non-sulphated mucoprotein, most likely sialomucin. Furthermore, it resists breakdown by hyaluronidase and diastase [5, 6]. These would importantly help to differentiate PMC from metastatic mucin-secreting breast carcinomas that express many similar proteins and receptors. The absence of epithelial cells with goblet-cell differentiation, the low molecular weight cytokeratin CK20 and dirty necrosis in combination would help in excluding a gastrointestinal source of metastasis [5].

Imaging (CT, MRI or PET scan) is an important modality in excluding other sources of metastatic mucin-secreting carcinomas to the skin before arriving at the diagnosis of PMC.

Wide local excision (WLE) is the treatment of choice [2]. Dissection of the loco-regional lymph nodes remains controversial if there is no suggestion of lymphatic spread [1, 2]. Mohs micrographic surgery is an alternative, allowing closer control of tissue excision – an important consideration in facial surgery. Adjunctive therapy could be used to reduce recurrence in first-instance PMC – hormonal therapy when oestrogen/progesterone receptor positive, radiotherapy in combination with WLE, and chemotherapy. However, in recurrent PMC, the efficacy of these therapies drops considerably.

PMC remains a diagnostic trap for the unsuspecting surgeon due to its benign-looking nature. It is vital to exclude metastasis to the skin. Once certain, WLE, whether in combination with lymph node dissection, and/or adjunctive therapy, should be undertaken. The patient then requires long-term follow-up due to the high recurrence rate.

Disclosure

References

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3 Breiting L, Christensen L, Dahlstrom K, et al. Primary mucinous carcinoma of the skin: a population-based study. Int J Dermatol 2008; 47: 242-5.

4 Headington JT. Primary mucinous carcinoma of skin: histochemistry and electron microscopy. Cancer 1977; 39: 1055-63.

5 Levy G, Finkelstein A, McNiff JM. Immunohistochemical techniques to compare primary vs. metastatic mucinous carcinoma of the skin. J Cutan Pathol 2010; 37: 411-5.

6 Kazakov DV, Suster S, LeBoit PE, et al. Mucinous carcinoma of the skin, primary and secondary: a clinicopathologic study of 63 cases with emphasis on the morphologic spectrum of primary cutaneous forms: homologies with mucinous lesions in the breast. Am J Surg Pathol 2005; 29: 764-82.