According to our report, we could put forward diagnostic criteria and therapeutic principles available for PI-DLBCL as follows: syndromes should include abdominal pain, abdominal distension, abdominal discomfort, or gastrointestinal bleeding; CD20(+) and Ki-67(+) should be detected from immunohistochemical staining; the treatment of proton pump inhibitor is ineffective; adenocarcinoma of duodenum should be excluded; R-CHOP chemotherapy is recommended as the first choice for treatment. The gene discussed is MKI67; the disease is adenocarcinoma.