Polypoid Kaposi Sarcoma Involving the Lower Gastrointestinal Tract: Clinicopathologic Study of 15 Cases

• Context.—Gastrointestinal manifestations of Kaposi sarcoma are rare but may cause morbidity. Lower gastrointestinal involvement is particularly rare, and lesions may resemble conventional bowel polyps. Objective.—To study 15 patients who presented with lower gastrointestinal tract Kaposi sarcoma with polypoid architecture. Design.—The surgical pathology files of the departments of pathology at multiple institutions were searched for cases of Kaposi sarcoma forming polyps in the lower gastrointestinal tract (jejunum, colon, rectum); 15 cases with such features were identified. Clinicopathologic information was extracted from the medical record and documented by reviewing individual hematoxylin-eosin–stained slides. Results.—The patients were 13 men and 2 women aged 26–80 years (median = 44 years). Gastrointestinal tract involvement was multifocal in 11 cases and unifocal in 4. The tumors involved the rectum, rectosigmoid junction, cecum, ascending colon, transverse colon, and descending colon and presented as polypoid lesions measuring 0.2–2.1 cm. Six patients had upper gastrointestinal tract involvement in addition to lower gastrointestinal lesions. Histologically, the tumors were characterized in 6 cases by a dense spindle cell proliferation in the lamina propria; however, the remaining cases showed only a subtle fascicular spindle cell proliferation in the lamina propria that did not form an expansile mass. Conclusions.—Biopsies of gastrointestinal polyps showing absence of the common features of hyperplastic or adenomatous polyps, particularly in immunocompromised patients, should be carefully examined for the presence of a stromal spindle cell proliferation. Use of immunohistochemical stains, particularly human herpesvirus-8, can help in establishing the correct diagnosis.