Treatment Stratification In B-Cell Ptld After Solid Organ Transplantation (Sot) By International Prognostic Index (Ipi) And Response To Rituximab: Interim Results From The Ptld-2 Trial.

8045 Background: The PTLD-1 trials have established risk-stratified sequential treatment of B-cell PTLD. After rituximab induction, patients (pts) in complete remission (25 %) received rituximab consolidation, while all others received R-CHOP. The PTLD-2 trial tests modified risk-stratification including clinical risk factors. These are the results of the 2nd scheduled interim analysis (40/60 planned pts). Methods: The prospective, multicenter phase II PTLD-2 trial (NCT02042391) enrols treatment-naïve adult SOT recipients with CD20-positive PTLD. Key exclusion criteria are CNS involvement, ECOG > 2, pregnancy, and severe organ dysfunction or severe, active infection. Treatment consists of rituximab (1400 mg SC; first application 375 mg/m2 IV) on days 1, 8, 15 and 22. After restaging, pts in CR as well as those in PR with ≤ 2 IPI risk factors at diagnosis (low-risk group) continue with four three-weekly courses of rituximab. Most other pts (high-risk group) receive 4 cycles of R-CHOP-21, while thoracic SOT recipients who progress under rituximab (very-high-risk group) receive six cycles of alternating R-CHOP-21 and R-DHAOx. The primary endpoint (event-free survival in the low-risk group) is not analyzed here. Secondary endpoints presented here are response and overall response (ORR) by computed tomography, overall survival (OS), time to progression (TTP) and treatment-related mortality (TRM) overall and by risk group. Results: 40 pts were recruited at 12 centers (2015 – 2019). 21/40 were kidney, 11 lung, 4 liver, 3 heart, and 1 liver/kidney transplant recipients. Median age was 54 years. 38/40 PTLD were monomorphic and 15/40 EBV-associated. 38 pts were evaluated for response at interim staging: 13 were allocated to the low-risk, 17 to the high-risk and 8 to the very-high-risk group. ORR was 28/30 (93 %, CR: 16/30 [53 %]). With a median follow-up of 1.9 years, the 1-year/3-year Kaplan-Meier (KM) estimates of TTP and OS in the intention-to-treat population (40 pts) were 85 %/80 % and 70 %/70 %, respectively. In the low-risk group, the 2-year KM estimate of OS was 100 %. The frequency of infections (all grades) was 50 %, and TRM occurred in 3/40 pts (8 %). Conclusions: One third of enrolled pts were treated in the low-risk group and the recruitment goal for evaluation of the primary endpoint will likely be reached. Interim efficacy and toxicity data with rituximab SC and modified risk-stratification are encouraging despite the inclusion of 35 % thoracic SOT recipients. Clinical trial information: NCT02042391 .