Abstract： Objective:To explore the predictive value of 18F-FDG PET/CT metabolic parameters combined with inflammatory markers for the medium-term efficacy of chemotherapy in patients with primary gastrointestinal diffuse large B cell lymphoma (PGI-DLBCL). Methods:From April 2011 to May 2020, 67 patients (37 males, 30 females, age: 28-85 years) with PGI-DLBCL examined by 18F-FDG PET/CT before chemotherapy in Changhai Hospital, Navy Medical University were retrospectively analyzed. All patients were treated with cyclophosphamide+ doxorubicin+ vincristine+ prednisone (CHOP) or rituximab+ CHOP (R-CHOP) regimens, and the medium-term efficacy was evaluated after 2-4 cycles of chemotherapy. The effect outcome was divided into complete remission (CR) group and non-CR (NCR) group based on the Lugano lymphoma response evaluation criteria. Mann-Whitney U test was used to compare the differences of SUV max, peak of SUV (SUV peak), metabolic tumor volume (MTV), total lesion glycolysis (TLG), platelet/lymphocyte ratio (PLR) and neutrophil/lymphocyte ratio (NLR) between two groups. The independent risk factors of NCR were analyzed by multivariate logistic regression and the binary logistic regression model was established according to the results. The model was tested with external validation data ( n=15). Results:Of 67 PGI-DLBCL patients, 28(41.8%) were CR and 39(58.2%) were NCR. SUV peak, MTV, TLG, PLR and NLR in NCR group (17.3(12.3, 28.1), 73.8(42.9, 141.7) cm 3, 887.5(300.9, 2 075.3) g, 203.9(155.7, 297.1), 3.9(3.0, 4.9)) were significantly higher than those in CR group (9.5(6.2, 15.2), 11.3(4.7, 23.2) cm 3, 85.2(35.5, 214.6) g, 149.3(102.8, 173.1), 2.2(1.8, 4.6); z values: from -6.41 to -2.33, all P<0.05). The logistic regression model was as follows: P=1/(1+ e - x), x=0.100×MTV+ 0.024×PLR-8.064. The prediction accuracy for NCR risk was 86.57%(58/67), with the accuracy of 13/15 tested by external validation data. Conclusion:MTV combined with PLR has a good predictive value for medium-term efficacy of CHOP/R-CHOP chemotherapy in patients with PGI-DLBCL.