Primary Extramammary Paget's Disease Following Previously Treated Secondary Extramammary Paget's Disease Over the Scrotum: A Rare Case Successfully Treated With Mohs Micrographic Surgery.

Extramammary Paget's disease (EMPD) is a rare cutaneous neoplasm that can be classified as either primary or secondary, depending on the presence or absence of an associated internal malignancy. Primary EMPD arises as an intraepithelial adenocarcinoma, while secondary EMPD results from the extension of an underlying visceral malignancy. This case report presents a unique instance of primary EMPD developing 10 years after a diagnosis of secondary EMPD in the same anatomical location, a phenomenon not previously documented in the literature. The patient, initially treated for secondary EMPD with wide local excision, later developed primary EMPD, as confirmed through histopathological and immunohistochemical analysis. This rare occurrence raises questions about the potential mechanisms, including field cancerization, persistent risk factors, or a coincidental event. The case underscores the importance of long-term follow-up and surveillance for EMPD patients. Mohs micrographic surgery remains the gold standard for treating EMPD due to its high precision in margin control and lower recurrence rates compared to conventional surgical methods. This case highlights the need for meticulous diagnostic approaches and continuous monitoring to manage and understand the complexities of EMPD effectively.