Eccrine Porocarcinoma Arising from a Benign Eccrine Poroma: A Rare Coexistence in a Single Lesion

Background: Eccrine Poromas (EPs) and Eccrine Porocarcinomas (EPCs) are rare adnexal tumors of the eccrine sweat glands, with EPCs representing the malignant counterpart. While EPCs may arise de novo, they can also develop from the malignant transformation of EPs, a process that remains poorly understood. The coexistence of both benign and malignant components within a single lesion is exceptionally rare, posing significant diagnostic challenges and emphasizing the importance of thorough histopathological evaluation. Case Presentation: We present a 72-year-old Asian male with a longstanding lesion on the lower right leg, the initial diagnosis was proposed as a squamous papillomatous lesion, the tumor was later classified as Squamous Cell Carcinoma (SCC) before a comprehensive histopathological review revised the diagnosis to EPC with coexisting EP. The malignant component demonstrated nuclear pleomorphism, increased mitotic activity and ductal differentiation, while the benign portion retained a uniform cellular architecture with no significant atypia. Immunohistochemical analysis confirmed ductal differentiation and supported the eccrine origin, emphasizing the role of histopathology and molecular markers in distinguishing EPC from SCC and other cutaneous neoplasms. Conclusion: This case underscores the complexities of diagnosing EPC, particularly in its coexistence with EP, reinforcing the need for meticulous histopathological and immunohistochemical assessment to avoid misdiagnosis. A review of the literature further contextualizes the clinical, histopathological and molecular findings, reinforcing the necessity of an interdisciplinary approach for accurate diagnosis and optimal management. As research into molecular markers and targeted therapies advances, this case highlights the ongoing need for standardized diagnostic guidelines and further investigation into the mechanisms of malignant transformation in eccrine tumors.