Association of Circulating Tumor DNA from the Cerebrospinal Fluid with High-Risk CNS Involvement in Patients with Diffuse Large B­-Cell Lymphoma

Diffuse large B­-cell lymphoma (DLBCL) patients with central nervous system (CNS) involvement have dismal outcomes. The detection sensitivity of conventional diagnosis of lymphoma through cerebrospinal fluid (CSF) cytology (CC) and flow cytometry (FCM) is restricted. CSF-ctDNA has shown to be an important method of liquid biopsy in patients with CNS cancers. To assess the correlation between CSF-ctDNA and CNS involvement in DLBCL, targeted mutational profiling was performed on CSF- and plasma -derived ctDNA together with matched systemic tumor tissues in 67 DLBCL patients clinically diagnosed as high risk for CNS relapse, using a validated panel of more than 400 genes. We found that ctDNA concentration in CSF but not in plasma correlated with CNS-IPI score in DLBCL patients. In CSF-positive high-risk DLBCL patients, eighty-six gene alterations(GAs) were shared between tumor tissue and CSF while ninety-five were shared between tumor tissue and plasma. Interestingly, forty-eight GAs(CSF-CNS GAs) were identified including 24 GAs exclusively in CSF and 24GAs shared by plasma which enriched in apoptosis/cell cycle related pathway and immunity-related pathway. To better screen for CNS-related molecular features in CSF, GAs in brain tumor tissue and CSF from a PCNSL-DLBCL cohort of 10 patients were sequenced and compared to that in high-risk group. Moreover, GAs in tumor samples from an additional cohort of 40 DLBCL patients clinically diagnosed as low-risk for CNS relapse were sequenced and compared to that in high-risk group to screen out non-CNS-related features. The number of alterations in five CSF-CNS genes including BTG2, PIM1, DUSP2, ETV6, CXCR4 in CSF was found to be associated with CNS risk in DLBCL patients. Our data supported the feasibility of using CSF-ctDNA as a complementary source for early detection of CNS involvement in DLBCL. The association between GAs in five CSF-CNS genes and CNS involvement deserved further investigation to determine their relevance in patient treatment and outcome.