e19058 Background: Follicular lymphoma (FL) was classified into three grades based on the number of centroblasts (FL1-2, FL3A, and FL3B). Guidelines suggest that FL1-2 should be treated according to the treatment recommendations for classical FL. FL3B is usually treated as diffuse large B-cell lymphoma (DLBCL).There is no consensus yet on the management of FL3A. In order to explore the relationship between clinical features and outcomes of FL3A, we conducted this study. Methods: We conducted a retrospective study of newly diagnosed FL patients who were admitted to our hospital from January 2013 to December 2022. The data were collected from the hospital electronic medical record system, including but not limited to: demographic characteristics, pathological information, clinical features at diagnosis, treatment, and efficacy evaluation. The survival curve was calculated through Kaplan-Meier method and compared with Log Rank test.The prognostic factors of PFS was compared by COX regression analysis. Results: There were 253 FL3A patients admitted, accounting for 27.55% of all FL patients. After screening, a total of 223 FL3A patients were included in this study. Among 223 patients, the male to female ratio was close to 1:1; The median age is 57 years old. At diagnosed, 33 patients in early stage and 190 in advanced stage. Among advanced patients, 144 had no treatment indications according to the GELF criteria. 86.1% (192/223) of patients received systemic treatment, with the majority of rituximab contained regimens. The overall response rate (ORR) was 96%, and 62.9% of patients who responded to chemotherapy received maintenance therapy with CD20 monoclonal antibody. A median follow-up of 41 months, with an estimated 5-year OS of 91.3% and 5-year PFS of 73%. The PFS of advanced FL patients treated with RCHOP regimen (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone) was significantly longer than that of non-RCHOP regimen patients (P<0.05). The PFS of patients receiving maintenance treatment was better than that of those not (P<0.05). Conduct prognostic analysis on advanced FL3A patients. Univariate analysis showed that treatment plan selection, maintenance of treatment, PET scan of FDG metabolic maximum uptake value (SUVmax), Ki-67, lactate dehydrogenase (LDH), white blood cell count (WBC), IgA, IgM, all significantly affected PFS; Multivariate analysis shows SUVmax ≥ 15 and platelet count<100 × 109/L and LDH>210U/L are all correlated with poor PFS. Conclusions: This study found that FL3A accounts for 27.55% of all FLs, with a median age of 57 years old and mostly in the advanced stage. FL3A has a long survival period, with a 5-year PFS of 73%. COX regression analysis showed that SUVmax, platelet count, and LDH were all associated with PFS in advanced FL3A patients.Those may explore new clinical prognosis prediction models.