UC Irvine

Abstract INTRODUCTION Primary CNS lymphoma is a rare aggressive hematological malignancy. Current chemotherapy for induction phase is HD-MTX single agent or HD-MTX based combination regimen. We report a rare case whose left and right parietal lymphoma lesions in the brain responded to different induction therapy regimens during the induction phase. CASE REPORT A 43-year-old female presented with seizure and her brain MRI showed bilateral parietal brain lesions in January of 2020. Biopsy and work-up revealed primary CNS diffuse large B-cell lymphoma (DLBCL). The patient underwent HD-MTX therapy. Brain MRI showed clear progression of left parietal lymphoma but stable right parietal lymphoma after two cycles of HD-MTX at 8 g/m2. The treatment was switched to a rituximab 750 mg/m2 weekly and temozolomide 150 mg/m2 daily one-week-on and one-week-off regimen. After 8 weeks, her brain MRI showed nearly complete response of her left parietal lymphoma to rituximab/temozolomide but progression of her right parietal lymphoma. She was switched back to HD-MTX and completed total 8 cycles. Her right parietal lymphoma lesion showed complete response to HD-MTX. The patient is doing well and has been off the treatment over the past 10 months and is waiting for consolidation therapy with autologous stem cell transplantation that has been postponed due to the COVID pandemic. DISCUSSION Our case highlights the very rare heterogenous feature of primary CNS lymphoma responding to different treatment regimen. Biopsy of bilateral heterogeneous lesions may be indicated to compare the different molecular features of the lymphoma to find underlying mechanism if they respond to treatment differently. Specific treatment regimen should be selected based on the responsiveness of CNS lymphoma lesions or combination therapy is selected to cover the heterogeneous susceptibility to chemotherapy regimens.