Pigmented Syringomatous Carcinoma/Sweat Gland Carcinoma of the Vulva With Melanocytic Colonization: An Uncommon Presentation of a Rare Sweat Gland Neoplasm

Primary vulvar carcinomas are rare and constitute a diverse group of neoplasms. These primary tumors are typically classified based on their presumed tissue of origin or histological characteristics. Among these, carcinomas of sweat gland origin are particularly significant. They closely resemble similar malignancies in nonvulvar skin, including various cutaneous adnexal-type cancers such as apocrine and eccrine adenocarcinomas. Syringomatous carcinoma of the vulva is a rare malignant sweat gland neoplasm known for its infiltrative growth and tendency for local recurrence. Typically, these malignancies manifest as nonulcerated nodules or plaques, primarily in the head and neck region. The occurrence of syringomatous carcinoma in the vulvar region is exceptionally rare. Herein, we present a unique case of a 35-year-old woman with a dark mole measuring 1.5 × 1.0 cm on the vulva. Complete excision was performed to exhibit an infiltrative haphazard proliferation of elongated ductules and tubules, displaying significant cytologic atypia characterized by irregular nuclear contours and variably prominent nucleoli. Extensive melanocytic pigment deposition and stromal fibrosis were also observed. Immunohistochemical staining demonstrated positive expression of epithelial markers, including keratins (AE1/AE3) and epithelial membrane antigen, supporting the diagnosis of syringomatous carcinoma. CK7 and carcinoembryonic antigen were negative, whereas SOX10 and pan melanin highlighted admixed, cytologically bland melanocytes within the epidermis and neoplastic nests. This case represents a highly unusual presentation of syringomatous carcinoma associated with melanocyte colonization. Due to limited data on the optimal management strategies, a multidisciplinary approach involving gynecologic oncologists, dermatopathologists, and radiation oncologists is essential for treatment decisions. Long-term follow-up is crucial, considering the potential for local recurrence and metastatic spread, emphasizing the importance of comprehensive clinical management for favorable patient outcomes of this rare malignancy.