Primary mucinous eccrine adenocarcinoma of the skin in a 69-year-old man

Introduction
Mucinous carcinoma of the skin is a rare tumor and could have either an eccrine or an apocrine origin from the deepest portion of the sweat duct (1). This normally asymptomatic and slow-growing tumor has demonstrated a local recurrence rate of 30% after excision with narrow surgical margins and can have rare chances of local or distant metastases. It is difficult to differentiate this tumor histologically from metastatic lesions (2-3).
The authors report a rare case of primary mucinous eccrine adenocarcinoma of the skin which was initially diagnosed as a metastatic adenocarcinoma in another center where they found no primary focus and the patient was treated with wide local excision and adjuvant radiotherapy. Two and a half year later after the initial treatment tumor recurred in the left axilla where it was first originated. After wide local excision of the lesion, the histopathologic diagnosis in our center was primary cutaneous eccrine mucinous adenocarcinoma.
We present the clinical, histological, and immunohistochemical features of this rare tumor in the light of the searched literature.

Case Report
A 69 years old man noticed a right axillary skin tumor and admitted to a hospital in January 2005. In this center the excision of the tumor was performed and then the axillary tumor was pathologically diagnosed as metastatic adeno-carcinoma. Therefore, he was searched for the primary focus. However, various imaging, endoscope, and pathological examinations revealed no tumor in the body. A blood laboratory test including tumor markers was almost normal. Hospital tumor community has decided to adjuvant radio-therapy with these findings. Tumor reoccurred in the same axilla after two and a half years from the initial treatment. At this time the patient admitted to our hospital. Macroscopically the mass on the right axilla was solitary, measured 15 mm in diameter, and protruded from the skin surface, asymptomatic, flesh-colored nodule without ulceration. Surgical wide tumor excision was performed.
Microscopically, the tumor was well demarcated from the surroundings, and located in the subcutaneous adipose tissue. Microscopically no connection between the tumor cells and epidermis was recognized. The tumor was also not communicated with any skin appendage structures (Fig. 1A). The tumor consisted of epithelial cell nests embedded in characteristic mucinous stroma (Fig. 1B) and was composed of monotonous polygonal epithelial cells without peripheral palisading. The tumor cell nests showed many luminal spaces, most of which connected with outer mucinous stroma like pseudo lumens (Fig. 1C). However, no apparent cribriform appearances were recognized. Cytologically, tumor cells were monomorphous, were polygonal or elongated in shape, and their cytoplasm was acidophilic (Fig. 1D). Their nuclei were hyperchromatic and showed irregularity of the shape, and discrete nucleoli were recognized in most of the tumor cells (Fig. 1D). Four to five mitotic figures were noted in 10 high power fields. Histo-chemically the mucinous stroma was strongly positive with PAS after diastase digestion and alcian blue stains at pH 2.5; the mucin was found consistent with sialomucin. The diagnosis was mucinous carcinoma. In fact, the incidence of metastatic mucinous carcinoma is much greater than that of primary mucinous carcinoma; therefore clinical history and detailed systemic evaluation is very important. A detailed systemic search of the patient was done including endoscope and radiological examinations which revealed no primary. According to histopathology findings, clinical history of the patient and results of the detailed systemic evaluation, diagnosis in our center was primary cutaneous eccrine mucinous adenocarcinoma.

Discussion
Primary cutaneous mucinous carcinoma was first documented by Lennox et al. (4). It is a rare tumor, occurs in head, neck, axilla and eyelid of elderly persons, and is more common in man than in woman (4, 5). It is a rare adnexal tumor that arises in the deep dermis and from the deepest portion of the eccrine secretory coil, the mucin-secreting dark cells. Snow et al reviewed 73 cases of primary cutaneous mucinous carcinoma and reported a median age at onset of 63 years and a male predominance of 2:1 (6) as our patient was 69 years old male. The lesions of mucinous carcinoma are usually slow-growing and the average size is 2 cm and has been isolated reports of ulceration (7, 8). Our patient had a 1.5 cm solitary, asymptomatic, flesh-colored nodule without ulceration. It is occasionally misdiagnosed as metastatic mucinous carcinoma as was in our patient. It is difficult to differentiate this tumor from metastatic lesions; metastatic deposits from mucinous carcinomas of the breast or gastrointestinal tract have an identical histomorphology. Primary mucinous carcinomas have shown positive cytoplasmic staining with S100, CEA, 35bH11 (low-molecular-weight cytokeratin), GCDFP–15, a-lactalbumin and also was estrogen receptor and progesterone receptor positive (9, 10). Unfortunately, any antibody profile is not specific to differentiate between primary mucinous carcinoma and a specific metastatic mucinous carcinoma (2). In fact, the incidence of metastatic mucinous carcinoma is much greater than that of primary mucinous carcinoma; therefore clinical history and detailed systemic evaluation is very important. In our patient we decided on the diagnosis of the primary tumor after a detailed systemic evaluation and clinical history of the patient.
Our patient who was misdiagnosed as metastatic mucinous adenocarcinoma in another center and was given radiotherapy to the axilla in spite of the fact that a primary origin could not been found. Radiotherapy and chemotherapy have not been effective in treatment of primary mucinous eccrine carcinoma (11). In our case tumor reoccurred in the axilla two and a half years later. The most frequent sites for mucinous carcinoma are as follows: eyelid (38%), face (other than eyelid) (20.3%), scalp (16%) and axilla (10%) (2). This normally asymptomatic and slow-growing tumor has demonstrated a local recurrence rate of 30% after excision with narrow surgical margins and can have local metastases (2). The rate of local metastasis to regional lymph nodes has been reported as 10% (2). Our patient has no lymph node metastases. Only 2 cases of distant metastasis have been reported thus far, one to the scalp and one to the axilla (11, 12). Risk factors for metastasis other than location are not known. However, the lesions are situated deep in the dermis; surgical margins of 1.5 to 2.0 cm are recommended for excision to prevent local recurrence. Alternatively, Mohs surgery is indicated to ensure clear margins in the cosmetically important areas like face. Magnetic resonance imaging has been used to assess the depth of a lesion on the cheek and may be helpful in planning surgical excision (13). In our patient one surgical margin was closer than 1mm but no reexcision was planned as systemic metastases are rare. He is still under control in every six months without local recurrence for more than one year.

References
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