Rectal syphilis: a great imitator of rectal malignancy.

A 48-year-old transgender woman presented with a sudden onset of bloody stool. Colonoscopy revealed an ulcerated, circumscribed mass in the lower rectum, closely resembling a Borrmann type 2 malignancy. The patient lacked classic signs of syphilis, such as anal pain, primary genital chancres, or localized lymphadenopathy. However, serological assays were highly reactive, and immunohistochemical analysis of the biopsy specimen confirmed the presence of Treponema pallidum, establishing the diagnosis of syphilitic proctitis. A four-week oral amoxicillin regimen (1,500 mg/day) led to complete clinical and serological resolution. This elusive condition must be considered when evaluating anorectal mucosal abnormalities.