摘要Objective: To determine the prevalence of Mycoplasma hyorhinis in archived paraffin-embedded gastric cancer tissue. Methods: The antigen recognized by anti-tumor monoclonal antibody PD4 was identified as P40 (a specific Mycoplasma hyorhinis protein). We constructed a tissue-microarray of high density containing 105 gastric cancer samples, 101 non-tumor margin samples and 62 benign gastric disease samples for detecting Mycoplasma hyorhinis using Immunohistochemistry. Results: The infection rate of M. hyorhinis was 54.1%(53/98) in gastric cancer samples, 51.7%(45/87) in non-tumor margin samples and 15.8%(9/57) in benign disease samples. The difference in infection rate between gastric cancer and benign gastric disease has statistical significance (P=0.001). Highly differentiated adenocarcinomas have a greater chance (84.6%) to be infected with M. hyorhinis than poorly differentiated ones (45.5%)(P<0.05. Conclusion: The infection rate of M. yorhinis was higher in gastric cancer than in other tastric diseases, which suggests the association between Mycoplasma infection and gastric cancer. Whether M. hyorhinis has oncogenic potential needs to be elucidated.