Background: Kaposi's sarcoma (KS) is one of the most common cancers in human immunodeficiency virus (HIV)-positive patients and leads to a high prevalence of morbidity and mortality. It usually appears as cutaneous or mucous lesions. Patients with visceral KS are asymptomatic and clinically silent. As the disease advances, patients may progress from a normal condition to exhibiting severe symptoms.

Case summary: A 27-year-old man presented with a 2-mo history of fever, bearing-down pain, and rectal bleeding. His hepatitis B virus DNA level was 2.7 ×10⁷ IU/mL. Abdominal computed tomography (CT) indicated liver cirrhosis. Before he was admitted to our hospital, he was diagnosed with HIV infection. His CD4 count was 24 cells/μL. Pelvic cavity CT suggested a thickened rectum wall accompanied by multiple enlarged lymph nodes. The patient was initially treated as having haemorrhoidal varices with bleeding, telbivudine for anti-hepatitis B virus treatment, and antibiotics for anti-infection. After half a month of treatment, the patient felt that his lower lumbus ache and bearing-down pain had not improved, and a colonoscopy was conducted. The result revealed a rectal mass that was histologically confirmed as KS with rectal spindle cells that were positive for cluster of differentiation 117 (CD117), CD34, human herpes virus 8, and CD31. He was administered systemic chemotherapy with 36 mg/d liposomal doxorubicin six times. The patient experienced no sign of lower gastrointestinal bleeding again.

Conclusion: This case highlights the diagnosis of primary KS with lower gastrointestinal bleeding in HIV-positive patients, which means visceral KS could not be excluded. The gold standard relies on colonoscopy and biopsy findings.