Background: Primary mediastinal B-cell lymphoma (PMBCL) is a rare subtype of aggressive B-cell lymphoma. The majority of relapses occur within the first few months resulting in a dismal prognosis, thus we need to identify the risk of early relapse. Circulating tumor DNA (ctDNA)-based response assessment may enable response adapted therapy and early prognostication. In this study, we aim to clarify the role of ctDNA-monitoring in early prediction of relapse.

Methods: We retrospectively analyzed the characteristics of 38 patients with PMBCL. The genetic sequencing and ctDNA monitoring were conducted by target next-generation sequencing (NGS).

Results: The median age was 32 years old and 26 (68.4%) were female. Most cases (31/38, 81.6%) were diagnosed with stage I or II disease and fourteen (36.8%) cases present with extranodal involvement. The 5-year PFS and OS for PMBCL patients were 65.7 and 72.1%, respectively. High IPI score were associated with poor survival by univariate analysis. The complete response (CR) rate and overall response rate of R-CHOP was similar to R-EPOCH (69.2% vs. 70.0%, P =1.000 and 84.6% vs. 95.0%, P =0.547, respectively), however the 5-year PFS and OS rate for R-EPOCH seems longer than those for the R-CHOP (PFS 82.9% vs. 53.8%, P=0.0569; OS 92.9% vs. 60.6%, P=0.0567). Radiotherapy was less delivered in the patients who received R-EPOCH than R-CHOP (5.0% vs.53.8%, P=0.003) and had no impact on prognosis. We performed genetic sequencing on twenty-three cases. STAT6(15/23, 65.2%), SOCS1(13/23, 56.5%), TNFAIP3(13/23, 56.5%) were the most common affected genes in both response and refractory/relapsed patients. Cell cycle, FoxO signaling pathway and TNF signaling pathway were more frequently involved in refractory patients. ctDNA monitoring was conducted in 16 cases and fifteen cases show undetectable ctDNA after a median of 2 (range from 1 to 5) cycles and one refractory case presented with durable positive ctDNA. Among 4 relapse cases, 3 had prior detectable ctDNA half a month earlier before imaging manifestations of relapse. Regarding prediction of relapse, positive predictive value of ctDNA is 100%.

Conclusions: Intensive induction chemotherapy can improve prognosis of PMBCL and ctDNA precisely predicted relapse. As most cases relapse within a few months, ctDNA-monitoring is crucial to improve prognosis.

Disclosures

No relevant conflicts of interest to declare.

Author notes

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Asterisk with author names denotes non-ASH members.