AIM: To clarify the diagnostic values of hematoxylin and eosin (HE), D2-40, CD31, CD34, and HHV-8 immunohistochemical (IHC) staining in gastrointestinal Kaposi’s sarcoma (GI-KS) in relation to endoscopic tumor staging. METHODS: Biopsy samples (n = 133) from 41 human immunodeficiency virus-infected patients were reviewed. GI-KS was defined as histologically negative for other GI diseases and as a positive clinical response to KS therapy. The receiver operating characteristic area under the curve (ROC-AUC) was compared in relation to lesion size, GI location, and macroscopic appearances on endoscopy. RESULTS: GI-KS was confirmed in 84 lesions (81.6%). Other endoscopic findings were polyps (n = 9), inflammation (n = 4), malignant lymphoma (n = 4), and condyloma (n = 2), which mimicked GI-KS on endoscopy. ROC-AUC of HE, D2-40, blood vessel markers, and HHV-8 showed results of 0.83, 0.89, 0.80, and 0.82, respectively. For IHC staining, the ROC-AUC of D2-40 was significantly higher (P < 0.05) than that of HE staining only. In the analysis of endoscopic appearance, the ROC-AUC of HE and IHC showed a tendency toward an increase in tumor staging (e.g. , small to large, patches, and polypoid to SMT appearance). D2-40 was significantly (P < 0.05) advantageous in the upper GI tract and for polypoid appearance compared with HE staining. CONCLUSION: The diagnostic value of endothelial markers and HHV-8 staining was found to be high, and its accuracy tended to increase with endoscopic tumor staging. D2-40 will be useful for complementing HE staining in the diagnosis of GI-KS, especially in the upper GI tract and for polypoid appearance. AIM: To clarify the diagnostic values ​​of hematoxylin and eosin (HE), D2-40, CD31, CD34, and HHV-8 immunohistochemical (IHC) staining in gastrointestinal Kaposi’s sarcoma (GI- KS) in relation to endoscopic tumor staging. METHODS: Biopsy samples (n = 133) from 41 human immunodeficiency virus-infected patients were. GI-KS was defined as histologically negative for other GI diseases and as a positive clinical response to KS therapy. The receiver operating characteristic area under the curve (ROC -AUC) was compared in relation to lesion size, GI location, and macroscopic appearances on endoscopy. RESULTS: GI-KS was confirmed in 84 lesions (81.6%). Other endoscopic findings were polyps (n = 9) 4), and malignant lymphoma (n = 4), and condyloma (n = 2), which mimicked GI-KS on endoscopy. ROC- AUC of HE, D2-40, blood vessel markers, and HHV-8 showed results of 0.83, 0.89, 0.80, and 0.82, respectively. For IHC staining, the ROC-AUC of D2-40 was significantly higher (P <0.05 In the analysis of endoscopic appearance, the ROC-AUC of HE and IHC showed a tendency toward an increase in tumor staging (eg, small to large, patches, and polypoid to SMT appearance). D2- 40 was significantly (P <0.05) advantageous in the upper GI tract and for polypoid appearance compared with HE staining. CONCLUSION: The diagnostic value of endothelial markers and HHV-8 staining was found to be high, and its accuracy tended to increase with endoscopic tumor staging. D2-40 will be useful for complementing HE staining in the diagnosis of GI-KS, especially in the upper GI tract and for polypoid appearance.