60 Persistent minimal contrast enhancement following autologous stem cell transplantation in primary CNS lymphoma

Abstract Introduction Primary CNS lymphoma (PCNSL) is a rare, aggressive form of extranodal non-Hodgkin’s lymphoma. High-dose methotrexate-based chemotherapy regimens have substantially improved PCNSL outcomes, but long-term survival remains unpredictable. The IPCG criteria guide semiquantitative response assessments by contrast-enhancing lesion measurement. This study investigated the association of persistent minimal contrast enhancement in PCNSL lesions with survival. Method Ethics permission was obtained for a retrospective study of serial MRI and clinical data (IRAS 326758). Inclusion criteria were: tissue diagnosis PCNSL; treated with MATRix chemotherapy; autologous stem cell transplant (ASCT) recipient; serial MRI for 2 years post-ASCT (or until death). Exclusion criteria were: incomplete imaging; no ASCT; death from non-PCNSL causes, and age >70 (fixed by MATRix eligibility). For each imaging time point, IPCG responses, residual enhancement size (mm²), duration of enhancement, and severity of T1 shortening (on a scale of mild, moderate, marked) were recorded. Statistical testing (Cox regression) was performed in SPSS (v29.0.2.0) with a p-value <0.05 considered significant. Results In n = 49 eligible cases, no survival disadvantage was observed for pre ASCT minimal enhancement (radiological CRu by IPCG) compared to complete response (CR). Post ASCT, a hazard ratio of 1.003 suggested a negligible (0.3%, p = 0.02) risk increase of disease progression with each time point of enhancement persistence. No relationship was identified between persistent enhancement diameters and OS/PFS (p > 0.9). In all patients (n = 11) with relapse during the study this progression was profound and distant, without any gradual deterioration of existing lesions. Conclusions We observed no impactful survival disadvantage for minimal contrast enhancement (IPCG category CRu) prior to ASCT or as a persistent imaging finding following ASCT compared to complete responders.