Extramammary Paget Disease (EMPD) is a rare intraepithelial cancer often mistaken for inflammatory and infectious skin conditions, leading to diagnostic delays and increased morbidity. It constitutes 6.5% of cutaneous Paget Disease, predominantly affecting older individuals aged 50 to 80, with a higher prevalence in women. Notably, 10% to 30% of EMPD cases are linked to concurrent visceral malignancies, highlighting the importance of cancer screening.

This is a case of a 77-year-old Filipino male with a four-year history of a solitary, well-defined, irregularly-shaped, erythematous plaque with erosions on the perianal area. Despite two years of self-administered hydrocortisone cream, the lesion progressively expanded into an 8x4x2 cm plaque, accompanied by intermittent pruritus and stinging pain. On consultation, dermoscopy showed milky-red areas, telangiectasias, and hyperpigmentation. Histopathology revealed polygonal neoplastic cells with pleomorphic vesicular nuclei, conspicuous nucleoli, and pale eosinophilic cytoplasm above the basal epidermis. Immunohistochemistry was positive for CK7, GCDFP15, CEA, and EMA, and negative for CK20. Further imaging showed no evidence of concurrent malignancies, reinforcing the diagnosis of primary EMPD. While awaiting further evaluation by other specialties, he was managed with an eight-week course of topical Imiquimod 5% cream, resulting in a reduction in both erythema and lesion thickness.

Overall, this case highlights the importance of recognizing cutaneous cancers that mimic benign skin conditions. The application of diagnostic tools in dermatology, such as dermoscopy, histopathology, and immunohistochemical staining, is crucial for identifying key disease features and establishing an accurate diagnosis, enabling timely and appropriate intervention.