Background: Relapsed/refractory PMBCL (rrPMBCL) generally has limited treatment options and dismal prognosis. Recently, monotherapy of anti-PD-1 was reported to induce an effective and durable clinical response in nearly half PMBCL patients. However, the use of anti-PD-1 alone is notably unpractical for those with bulky aggressive lesions or life-threatening tumor mass given that anti-PD-1 alone always induce delayed tumor degradation. This ongoing, phase I/II study was aimed to evaluate the safety and efficacy of GVD chemo-regimen plus anti-PD-1 (SHR-1210) with or without low-dose decitabine priming in rrPMBCL patients with bulky aggressive lesions. Methods: This trial is enrolling patients with rrPMBCL who have bulky disease (minimum measurement must be > 75 mm in the longest diameter) with aggressive phenotype, rapid progression and fatal prediction. Enrolled patients were randomizedly assigned into 2 salvage treatment cohorts: GVD (Gemcitabine 0.8 g/m²,Vinorelbine 30 mg/d, Doxorubicin 20 mg/m² , day 1, per 3 weeks) plus SHR-1210 (4 mg/kg, day 2, per 3 weeks) with (cohort 1) or without (cohort 2) low-dose decitabine priming (10mg/d, day -1 to -5, per 3 weeks). Safety was assessed by CTCAEv4.0, and clinical response by International Working Group (IWG) Response Criteria. Results: The prominent adverse event is ≤Grade 3 hematotoxicity in cohort 1. All enrolled 18 heavily-pretreated PMBCL patients had an effective control of disease progression after 1-cycle treatment and no death incident occurred so far. 11 patients had completed 4- to 8-cycle treatment, among them, 7 from cohort 1 were 2 CR, 4 PR, and 1 SD; 4 from cohort 2 were 3 CR and 1 PR. 6 patients who finished 8-cycle treatment had a 6- to 10-month ongoing progression-free survival so far. Conclusions: Both 2 regimens had comparably life-saving and durable clinical efficacy. Although all observed adverse events were tolerable in both groups, patients enrolled in the future will by treated by regimen without decitabine in view of the relatively lower treatment-associated toxicities. Clinical trial information: NCT03346642