Eccrine carcinoma (EC) is a rare carcinoma that originates from the eccrine sweat glands of the skin and accounts for less than 0.01% of diagnosed cutaneous malignancies. Sweat gland tumors have traditionally subdivided into four broad groups: eccrine, apocrine, mixed origin (eccrine and apocrine) and other un-classifiable sweat gland tumors. Eccrine tumors further divide into benign and malignant. Benign entities include poroma, hidradenoma, spiradenoma, cylindroma, syringometaplasia, syringoma, syringofibroadenoma, and chondroid syringoma. Malignant eccrine carcinoma entities include porocarcinoma, hidradenocarcinoma, malignant spiradenoma carcinoma, malignant cylindroma, syringoid eccrine carcinoma, microcystic adnexal carcinoma, mucinous carcinoma, adenoid cystic carcinoma, and ductal papillary adenocarcinoma. Other un-classifiable sweat gland tumors include eccrine ductal carcinoma, basaloid eccrine carcinoma, clear cell eccrine carcinoma and non-specified sweat gland carcinomas.
Malignant sweat gland tumors are heterogeneous neoplasms of different biological behavior. The principal characteristic of these tumors is that they are locally aggressive and show a high rate of recurrence. Separation of eccrine carcinoma has traditionally been according to their behavior into low grade and high grade malignant. Proper identification of eccrine carcinoma is sometimes challenging due to the morphological similarity to other common tumors and the lack of consistent immunohistochemical markers.
Research has not uncovered a clear etiology.
Eccrine carcinoma is an extremely rare cutaneous malignancy that accounts for less than 0.01% of diagnosed cutaneous malignancies
Sweat gland tumors divide into eccrine, apocrine, mixed origin (eccrine and apocrine) and other un-classifiable sweat gland tumors. In real practice, most sweat gland tumors have both eccrine and apocrine components. Some even show complexity such as showing other lines of differentiation, namely follicular and/or sebaceous. This differentiation is possibly due to the close embryological relationship between apocrine glands and pilosebaceous units. Histopathologies closely associated with eccrine carcinoma include hidradenocarcinoma, spiradenocarcinoma, and porocarcinoma.
Some relatively important and common types of eccrine carcinoma include porocarcinomas, syringoid carcinoma, ductal carcinomas, adenoid cystic carcinomas, and mucinous carcinomas. Porocarcinomas are characteristically solid neoplastic lobular masses with cystic changes and necrosis. Two types of atypical cells are present in porocarcinomas: eosinophilic and clear cells. These tumor cells are usually positive for cytokeratin and PAS. Syringoid carcinoma shows a mix of tubules, keratinizing cystic structures, solid islands, cellular cords, and desmoplastic stroma, resembling syringomas to some extent. Ductal carcinomas characteristically demonstrate by the presence of tubular structures mixed with variable amounts of cellular cords. The degree of differentiation range from well to poorly differentiated. Tumor cells are positive for PAS, D-PAS and, cytokeratins. Adenoid cystic carcinomas are morphologically composed of basaloid and monomorphous cells; moderately atypical with hyperchromatic nuclei and inconspicuous cytoplasm. Tumor cells typically arrange in cribriform masses, islands, and tubular structures. Mucinous carcinomas are morphologically composed of cells, arranged in solid islands, cribriform masses, tubules, and small nests embedded in large mucin pools.
Immunohistochemistry and molecular genetics play only a minor role in the diagnosis of sweat gland tumors, however, can be useful in excluding other possible entities. One relevant entity to exclude is cutaneous metastases from visceral primary adenocarcinomas. When pathological complexity is evident, and the pathologist cannot fit the case to any established category, they should render a descriptive diagnosis of benign/malignant tumor with sweat gland differentiation.
The test of choice in the diagnosis of eccrine carcinoma is skin biopsy. The biopsy will show infiltrative, moderately to poorly differentiated neoplasm in a nested to the trabecular pattern. Nuclei are relatively uniform with notably prominent nucleoli. The specific morphology depends on the distinct eccrine carcinoma entity. Relatively common types of eccrine carcinoma include porocarcinomas, syringoid carcinoma, ductal carcinomas, adenoid cystic carcinomas, and mucinous carcinomas. Immunohistochemistry (IHC) may be helpful in some cases; however, it is inconsistent. Markers that can support an EC diagnosis include carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA), estrogen receptors (ER), progesterone receptors (PR), cytokeratin 7 (CK-7), and pancytokeratins.
Eccrine carcinoma pathologically stages (pTNM) as follows:
Primary Tumor (pT)
Regional Lymph Nodes (pN)
Distant Metastasis (pM)
Metastatic disease shows poor prognosis. The relative mortality rate is 80%, and the 10-year disease overall survival rate is 9%.
Eccrine carcinoma complications include metastases and/or adverse effects related to surgical intervention.
Patients should receive education regarding the prognosis and the possible adverse side effects of surgical intervention before beginning treatment.
Eccrine carcinoma is an extremely rare cutaneous malignancy. The prognosis is overall favorable in localized early lesions, however an unfavorable prognosis in metastatic lesions. Eccrine carcinoma needs a multidisciplinary management approach with a medical oncologist, surgeon, dermatologist, dermatopathologist, pharmacist, and oncology nurse all playing a role in the management of the condition and working collaboratively to bring about optimal patient treatment and outcomes. [Level V]
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