A Case of Unusual Clinical Presentation and Progression of Endocrine Mucin-Producing Sweat Gland Carcinoma

INTRODUCTION

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is an uncommon, low-grade skin tumour that predominantly occurs in the head and neck area, with a notable preference for the eyelid. EMPSGC, first identified as a distinct entity in the late 1990s, is defined by its neuroendocrine differentiation, slow-growing clinical behaviour, and mucin production.^[1] In 2018, the World Health Organisation (WHO) Classification of Skin Tumours officially acknowledged EMPSGC, suggesting that hybrid lesions containing both in situ and invasive mucinous components be classified as mucinous adenocarcinoma with neuroendocrine features.^[2] Although EMPSGC generally has a good prognosis, the potential for recurrence at the original site and the uncommon occurrence of metastasis, especially in cases affecting the scalp with neck involvement, underscores the importance of accurate histopathological diagnosis and extended clinical monitoring.

CASE REPORT

Over 3 years, a progressively enlarging, pruritic scalp lump developed in a 58-year-old female with diabetes, hypertension, and ischaemic heart disease. She also experienced mild pain on the scalp, along with a non-enlarging left-sided neck lump. Physical examination revealed a 3 cm round, pink-red scalp nodule and a nodule on the posterior aspect of the neck on the left side, which was 2cm in diameter, firm and mobile.

After excision, the specimen was a skin ellipse with subcutis showing an ill-defined lesion [Figure 1] and a separate nodule sent as a neck lymph node showing muscle fibres with similar lesions. Histopathological analysis showed [Figures 2a and 2b] a deep dermal to subcutaneous large non-encapsulated tumour with areas of delineation/pushing borders, as well as infiltrative foci. The tumour displayed well-demarcated expansible nodules with solid and cribriform architecture in addition to small nests. A characteristic focal neuroendocrine morphology was observed.

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Figure 1:

(a): Skin ellipse with a nodular lesion, (b): Cut surface showing a pale white, fleshy, infiltrative neoplasm.

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Figure 2:

(a) Dermal tumor with infiltrating borders (H&E; 4x), (b) Neuroendocrine features (H&E; 10x), (c) Synaptophysin positivity (IHC; 10x), (d) Estrogen receptor positivity (IHC; 10x). IHC: Immunohistochemistry, H&E: Haematoxylin and eosin stain.

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A diagnosis of EMPSGC that progressed to mucinous adenocarcinoma was made based on the immunohistochemistry (IHC) findings [Figures 2c and 2d]. The neoplastic cells exhibited positivity for cytokeratin (CK7), synaptophysin, CGA, and the oestrogen receptor.

DISCUSSION

A rare condition first described in 1997, EMPSGC typically involves the periocular skin and affects females in their 6th or 7th decades.^[3] Identifying EMPSGC or its association with mucinous sweat gland carcinoma (MSC) depends on a combination of distinct neuroendocrine morphology, clinical characteristics, and positive neuroendocrine staining. The full IHC profile, which includes positive staining for oestrogen and progesterone receptors (ER/PR), also plays a role in establishing the diagnosis.^[4]

Authors advise excluding the possibility of secondary metastases in all EMPSGC cases, particularly from mucinous neuroendocrine carcinoma of the breast, as they exhibit similar morphology and share positivity for markers like ER/PR. This step involves imaging modalities like mammography.^[5]EMPSGC is considered indolent, with no reported metastases, though recurrences may occur.^[6] Although the risk of recurrence or metastasis is low, these tumours can cause significant local destruction and cosmetic disfigurement.^[2]

A thorough excision of the lesion is a crucial intervention to reduce the likelihood of recurrence or progression to invasive carcinoma. Increasing awareness of EMPSGC and its association with MSC is essential for improving diagnostic accuracy. Understanding key characteristics such as age of onset, sex predilection, and distinct morphological features can facilitate earlier and more precise identification of these tumours.^[6]

CONCLUSION

Diagnosis of cutaneous adnexal tumours, particularly sweat gland tumours, is challenging due to their rarity, inconsistent nomenclature, and overlapping terminologies. This case report highlights an exceptionally rare neoplasm with an unusual clinical presentation. Histopathology remains the diagnostic gold standard, aided by immunological and clinico-radiological correlations. Carcinoma diagnoses-related unnecessary psychological stress can be reduced, and crucial prognostic benefits can be obtained by earlier and accurate diagnosis of EMPSGC and associated MSC.