|Year : 2014 | Volume
| Issue : 2 | Page : 90-93
Squamoid eccrine ductal carcinoma: A diagnostic challenge
Jayashree Krishnamurthy1, Lopa Mudra Kakoti1, Ravishankar Nagaraj2
1 Department of Pathology, JSS Medical College, JSS University, Mysore, Karnataka, India
2 Department of Surgery, JSS Medical College, JSS University, Mysore, Karnataka, India
|Date of Web Publication||18-Dec-2014|
#1670, 7th Cross, NS Road, Mysore, Karnataka
Source of Support: None, Conflict of Interest: None
Squamoid eccrine ductal carcinoma (SEDC) is a rare primary cutaneous tumor that exhibits both squamous and adnexal ductal differentiation. We report a case of SEDC presenting as multiple nodules on the scalp of a 58-year-old man. Histopathological examination of the excised lesion showed a tumor in the dermis composed of duct-like structures that represented the eccrine component and squamoid cells in nests and in an infiltrating pattern. Immunohistochemical (IHC) positivity for cytokeratin 5/6, epithelial membrane antigen (EMA), and p63 confirmed the squamoid, ductal, and primary cutaneous nature, respectively, and differentiated it from eccrine poroma, microcystic adnexal carcinoma, and porocarcinoma with squamous differentiation. With a demonstrated invasive potential, recurrent nature, and ambiguous metastatic potential, Mohs micrographic surgery, an established and successful, yet tissue-sparing surgical modality with lower recurrence rate, is the recommended treatment of choice and a close follow-up of these patients is suggested for further experiences of this tumor.
Keywords: Biphenotypic carcinoma, cutaneous nodule, eccrine carcinoma, indeterminate malignant potential, squamous cell carcinoma
|How to cite this article:|
Krishnamurthy J, Kakoti LM, Nagaraj R. Squamoid eccrine ductal carcinoma: A diagnostic challenge. Indian J Dermatopathol Diagn Dermatol 2014;1:90-3
|How to cite this URL:|
Krishnamurthy J, Kakoti LM, Nagaraj R. Squamoid eccrine ductal carcinoma: A diagnostic challenge. Indian J Dermatopathol Diagn Dermatol [serial online] 2014 [cited 2019 Apr 20];1:90-3. Available from: http://www.ijdpdd.com/text.asp?2014/1/2/90/147313
| Introduction|| |
Squamoid eccrine ductal carcinoma (SEDC) is a rare primary cutaneous tumor that exhibits both squamous and adnexal ductal differentiation.  Till date, only nine cases of SEDC have been reported in the literature.  The cell of origin of these tumors is controversial, as it may represent squamous cell carcinoma (SCC) arising from eccrine ducts or a subtype of eccrine carcinoma (EC) with extensive squamoid differentiation or it could represent a biphenotypic carcinoma. , They have been classified both as variants of cutaneous SCC and as a type of EC.  SEDC often presents in the middle-aged or elderly as a hard, usually non-ulcerated, single or multiple cutaneous nodules and shows a predilection for the head, neck, and extremities.  The tumors are generally poorly circumscribed and show an infiltrative growth pattern with a deep extension into the dermis and subcutaneous tissues.  The histological features include duct-like structures resembling the dermal part of the eccrine duct and atypical squamous cell clusters.  As these lesions have an indeterminate malignant potential, attention has been directed toward making a definitive histological diagnosis for an effective potential therapy that minimizes the risk of recurrence or metastasis.  We hereby report a case of SEDC that presented as multiple swellings over the scalp.
[TAG:2]CASE REPORT [/TAG:2]
A 58-year-old man presented with history of two gradually increasing nodules on the scalp since 3 months. On examination, the two nodules over the scalp were of 1 × 1 cm each and one of them showed a punctum-like area in the center which prompted to arrive at a clinical diagnosis of sebaceous cyst. Both the nodules were excised completely and subjected to histopathological examination. Microscopically, the sections from both the nodules revealed tumors in the dermis composed of duct-like structures and squamoid cells in nests and in an infiltrating pattern [Figure 1]. The cells lining the ducts showed moderate pleomorphism and had vesicular nuclei and prominent nucleoli [Figure 2]. The squamoid cells had abundant eosinophilic cytoplasm and large, irregular hyperchromatic nuclei. They were seen infiltrating into the deep dermis and were forming squamous eddies at places [Figure 3]. There was dermal sclerosis and perineural infiltration seen in the periphery. Immunohistochemically, the lesion was positive for cytokeratin (CK) 5/6 [Figure 4], epithelial membrane antigen (EMA) [Figure 5], and p63 [Figure 6]. The resected margins of both lesions were free of tumor and no further treatment was administered. The patient is being followed up for the past 6 months and has no recurrence.
|Figure 1: Section from the scalp nodule displaying a tumor in the dermis composed of duct-like structures and squamoid cells in nests and in an infiltrating pattern. (H and E, X10)|
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|Figure 2: Ductal cells displaying moderate pleomorphism, vesicular nuclei, and prominent nucleoli. (H and E, X20)|
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|Figure 3: Squamoid cells displaying pleomorphism, forming squamous eddies and infiltrating the deep dermis. (H and E, X40)|
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|Figure 4: Immunohistochemically, the squamoid cells are positive for cytokeratin|
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|Figure 6: Immunohistochemically, the lesion is positive for p63 indicating a primary cutaneous tumor|
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| Discussion|| |
SEDC is a rare entity and is one among the diverse variants of ECs, with the others being a spindle cell variant with myoepithelial differentiation, a basal cell carcinoma like variant, and a variant with abundant fibromyxoid stroma.  It was first reported by Wick and Swanson as a subtype of EC with prominent squamoid differentiation, which poses a potential diagnostic pitfall as it can be easily misdiagnosed as SCC.  Similar to the present case, the lesion often presents as a slowly growing cutaneous nodule in the middle-aged or elderly individuals. ,
Histologically, SEDC is a poorly circumscribed infiltrative lesion composed of duct-like structures resembling the dermal part of the eccrine duct and atypical squamous cell clusters that form squamous eddies and horn cysts in the upper part, while the deeper component shows cells arranged in small infiltrative nests and cords. , Squamoid eccrine ductal carcinoma should be considered in the differential diagnosis of cutaneous adnexal neoplasms showing squamoid and ductal features of differentiation. 
The significance of the diagnostic dilemma lies in the disparity of clinical behavior between SCC and EC. Eccrine adnexal tumors are characterized by multiple local recurrences in 70-80% of cases, perineural invasion, and in approximately 50% of cases, they metastasize to regional lymph nodes and/or to different visceral organs. , SEDC is deeply infiltrative and poses a diagnostic challenge in superficial shave biopsies of skin. 
Despite having been largely classified as an eccrine tumor with a potential for perineural and perivascular invasion, literature suggests that unlike eccrine tumors which are known to be highly aggressive, SEDCs behave less aggressively. This conclusion is, however, tempered by the dearth of cases that have been reported. 
Immunohistochemically, as in the present case, the lesion being positive for CK 5/6 and/or 17 highlights the squamoid nature while the positivity of EMA and/or carcinoembryonic antigen (CEA) highlights the ductal structures. Positivity of p63 points toward a primary cutaneous origin, while low levels of Ki67 and p53 are consistent with a low-grade tumor. 
Given the lesion's intermediate malignant potential, attention has been directed toward the pitfalls of definitive histological diagnosis and the most effective potential treatment to minimize the risk of recurrence or metastasis.  The differential diagnosis for SEDC includes SCC, metastatic carcinoma with squamoid features, and eccrine tumors including eccrine poroma, microcystic adnexal carcinoma (MAC), and porocarcinoma with squamous differentiation. ,
The immunohistochemical (IHC) profile of eccrine neoplasms includes positivity for S-100, EMA, CKs, and CEA.  Positive staining with EMA and CEA is typical of glandular tissue and is supportive of an adnexal origin, as the aforementioned markers are typically negative in epithelial malignancies such as SCC. IHC has additional utility in demonstrating the combination of P63 and CK5/6 positivity in order to delineate primary from metastatic adenocarcinoma in the skin. 
Limited information is available about the management of SEDC because of its rarity.  For a definitive treatment of ECs, surgical extirpation with complete margin examination is recommended as the lesion tends to be underestimated in its size, is aggressive in its infiltration, and has a proclivity for perineural and perivascular invasion. Mohs micrographic surgery (MMS), the established and successful surgical procedure followed in a variety of cutaneous malignancies, is recommended as it is proven to be effective, yet tissue sparing and has a lower recurrence rate than the other treatment modalities. , Thus, given the uncertainty of SEDC's etiology, malignant taxonomy with pathologically demonstrated invasive potential, recurrence rate, and ambiguous metastatic potential, it is important for the physicians to be aware of this entity to arrive at a proper diagnosis. Also, further experiences with this tumor are necessary and a close follow-up of these patients is suggested.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]