Lymphogranuloma venereum (LGV) is a sexually transmitted infection caused by Chlamydia trachomatis serotypes L1–L3. It's incidence has been increasing in recent years, particularly among men who have sex with men with concomitant HIV infection, often associated with high-risk practices such as chemsex. Clinical presentation frequently involves proctitis and can mimic neoplastic disease, leading to diagnostic challenges.

We report the case of a 45-year-old HIV-positive male on antiretroviral therapy with undetectable viral load and CD4 count of 270. He presented with a 20-day history of diffuse abdominal pain, predominantly in the left hemiabdomen, hyporexia, abrupt constipation, 5 kg weight loss, and self-limiting rectal bleeding. Abdominopelvic CT revealed heterogeneous rectal wall thickening highly suggestive of malignancy. Colonoscopy showed findings compatible with infectious proctitis, without suspicious neoplastic lesions. Biopsies and microbiological studies were obtained, and PCR testing confirmed C. trachomatis serotype L2b, consistent with LGV.

In conclusion, LGV is an underdiagnosed re-emerging infection whose presentation may simulate malignancy. Clinician awareness, early colonoscopy, and appropriate sampling are crucial for timely diagnosis and treatment.