Relapsed and refractory primary CNS lymphoma: treatment approaches in routine practice.

Despite recent therapeutic progress and improved survival for many patients with primary central nervous system lymphoma (PCNSL), up to 50% of patients will experience refractory or relapsed disease following first-line treatment with high dose methotrexate (HD-MTX) based regimens. The majority of such events occur within 2 years of diagnosis although, unlike their systemic counterpart, the risk of PCNSL relapse remains, even for patients in radiologic complete response at 10 years following diagnosis. Currently, there are no approved therapies, and no widely accepted 'standard-of-care' approaches for the treatment of refractory or recurrent primary central nervous system lymphoma (rrPCNSL). Re-treatment with HD-MTX based regimens, use of non-cross resistant chemotherapy regimens, high-dose chemotherapy and autologous stem cell transplantation (HDT-ASCT), and brain irradiation all remain important therapeutic approaches for rrPCNSL. However, the survival outcomes for patients with rrPCNSL remain extremely poor and the vast majority of patients will die of their disease. Increasingly, novel treatment approaches are being investigated in early phase clinical studies. Importantly, such therapies need to be evaluated in the context of both refractory and relapsed disease; in older patients and those with co-morbid conditions; and those with neurocognitive dysfunction. A deeper understanding of the molecular genetic mechanisms underpinning rrPCNSL and its unique tumor microenvironment is urgently needed to inform biologically rational and effective therapies. rrPCNSL remains a clear unmet clinical need and a high priority area for clinical research that will require national and international collaborative studies with embedded translational science in order to improve outcomes for patients.