Supplementary Material for: Perianal Rhabdomyosarcoma Mimicking Perianal Abscess: Case Report and Literature Review

Introduction Perianal rhabdomyosarcoma (RMS) is an exceedingly rare and aggressive soft tissue malignancy that can mimic benign conditions, such as perianal abscesses, which complicates its diagnosis and treatment. This study reports a case of perianal RMS and discusses the management approach and the challenges in diagnosis. Presentation of case A 26-year-old woman with a past medical history of breast cancer, treated with partial mastectomy, chemotherapy, and radiation therapy, presented with a recurrent perianal mass initially drained multiple times for presumed abscesses. Upon further evaluation, physical examination revealed a 7 cm perianal wound with purulent and bloody discharge. Imaging studies revealed a lobulated mass in the perineal area with involvement of the anus. Biopsy confirmed the diagnosis of alveolar RMS (ARMS). The patient was treated with six cycles of neoadjuvant chemotherapy, followed by excisional biopsy. The tumor was resected with clear margins and Immunohistochemical (IHC) analysis confirmed the diagnosis. Adjuvant chemotherapy was initiated, and the patient remains asymptomatic at six-month follow-up. Conclusion Rhabdomyosarcoma should be considered in the differential diagnosis of perianal masses, especially in cases with recurrence