Assessment of Circulating Tumor DNA in Newly Diagnosed DLBCL Patients Randomly Treated By R-CHOP or R-High Dose Chemotherapy Plus Autologous Stem Cell Support

Purpose Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin's lymphoma. The association of rituximab to CHOP chemotherapy is nowadays the standard of care for de novo DLBCL patients; however 40% of these patients relapse or are refractory to treatment within 2 years. Before rituximab, patients treated by high dose chemotherapy plus autologous stem-cell support (HDT) had a significantly better outcome than by CHOP alone 1. Between 2005 and 2008, the GOELAMS 075 French multicentric clinical trial (NCT00561379) enrolled 323 de novo DLBCL patients randomly treated by R-CHOP or R-HDT, and showed that rituximab erases the survival difference between the two arms of frontline treatment 2. The main objective of this study was to evaluate circulating tumor DNA (ctDNA) concentration measured by an easy-to-collect and cost-effective method in the GOELAMS 075 de novo DLBCL patients, in regards of the two frontline treatments. Methods Plasma samples were collected at inclusion for 123 patients and 6 months after the end-of-treatment (EOT) for 50 patients in complete remission (CR) at EOT. The 123 patients were representative of the 323 eligible patients. Among the 123 patients, 68 were assigned to the R-CHOP arm and 55 to the R-HDT arm, of which, respectively, 59 and 51 achieved CR at EOT. Baseline characteristics, overall (OS) and progression free survivals were not different between randomization arms for the 123 patients. No difference in baseline characteristics was found between both studied cohorts. ctDNA concentration in ng per ml of plasma was measured as the enrichment of DNA fragments between 100 and 300 base pairs. For survival analysis, the ctDNA threshold was defined as equal to 10 times the maximum cell-free DNA concentration measured in healthy subjects. For paired samples, mutation profiles at baseline and 6 months after EOT were assessed by capture-based targeted DNA sequencing using a panel of 43 genes known to be associated to DLBCL in the literature. Intention-to-treat (ITT) analysis was performed, unless otherwise mentioned. Results Elevated ctDNA at diagnosis was found significantly associated with adverse clinical factors (R-IPI ≥3 ; number of extranodal sites ≥2), as well as intake of salvage therapy. Patients with ctDNA ≥ 54.9 ng/ml had significantly worse OS (HR=2.4, 95 th CI : 1.1-5.2 ; Pvalue=0.029). Patients with elevated ctDNA were more likely to require a salvage therapy, regardless of the randomisation arm. Only for ITT R-CHOP patients, elevated ctDNA was associated with a significantly shorter OS (HR=4.4, 95th CI : 1.6-12.3 ; Pvalue=0.004; Figure 1). Patients with elevated ctDNA who received the initially planned 8 R-CHOP cures (no salvage therapy) had a significantly worse OS than any other patients (67% deaths ; 5-years OS : 33% ; Pvalue=0.0002). Focusing on the cohort of 50 patients in CR at the EOT, we found a significant decrease of ctDNA 6 months after EOT compared to baseline only for ITT R-HDT patients (Pvalue=0.006). Noticeably, out of the 7 patients with higher ctDNA 6 months after EOT, six had been assigned to the R-CHOP arm, and five of those did not benefit salvage therapy. Mutation profiling was performed for 46 CR patients (ITT, R-CHOP, n=23 ; R-HDT, n=23) at baseline and 6 months after EOT. Mutations were detected in 48% of R-CHOP patients and 61% of R-HDT patients. The tumor mutational burden, defined as the number of gene mutations found on the total of 164 Kb sequenced, was significantly decreased 6 months after EOT only for R-HDT patients (Pvalue=0.005). The number of mutations, especially the number of new variants, and the number of deleterious and likely oncogenic variants, increased significantly in the R-CHOP arm 6 months after EOT while decreasing in the R-HDT arm (Pvalue<0.001; Figure 2). All 46 patients in CR at EOT remained in CR 5 to 10 years after treatment, except for 3 patients, who did not receive salvage therapy and relapsed more than 5 years after EOT. All 3 patients belonged to the R-CHOP arm patients with higher ctDNA 6 months after EOT compared to baseline. Conclusion Using an easy-to-measure and low-cost method, ctDNA concentration at diagnosis was shown, in an intention-to-treat analysis, to be an adverse prognostic factor only for de novo DLBCL patients treated by standard R-CHOP. Furthermore ctDNA was not significantly cleared in plasma at CR only for ITT R-CHOP patients, with the number of mutations increased 6 months after EOT compared to baseline. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

The CXCL12 Crossroads in Cancer Stem Cells and Their Niche

Cancer stem cells (CSCs) are defined as a subpopulation of “stem”-like cells within the tumor with unique characteristics that allow them to maintain tumor growth, escape standard anti-tumor therapies and drive subsequent repopulation of the tumor. This is the result of their intrinsic “stem”-like features and the strong driving influence of the CSC niche, a subcompartment within the tumor microenvironment that includes a diverse group of cells focused on maintaining and supporting the CSC. CXCL12 is a chemokine that plays a crucial role in hematopoietic stem cell support and has been extensively reported to be involved in several cancer-related processes. In this review, we will provide the latest evidence about the interactions between CSC niche-derived CXCL12 and its receptors—CXCR4 and CXCR7—present on CSC populations across different tumor entities. The interactions facilitated by CXCL12/CXCR4/CXCR7 axes seem to be strongly linked to CSC “stem”-like features, tumor progression, and metastasis promotion. Altogether, this suggests a role for CXCL12 and its receptors in the maintenance of CSCs and the components of their niche. Moreover, we will also provide an update of the therapeutic options being currently tested to disrupt the CXCL12 axes in order to target, directly or indirectly, the CSC subpopulation.

MBCL-17. METASTATIC MEDULLOBLASTOMA CAN BE CURED WITHOUT EXCISION OF THE PRIMARY TUMOR: A SINGLE CENTER EXPERIENCE

INTRODUCTION Metastatic medulloblastoma is a challenging disease The current clinical approach advocates removal of the primary tumor in the posterior fossa despite evidence of metastatic disease and administer oncologic treatment within several weeks: Infants of 3–4 years are treated by tandem high dose chemotherapy with stem cell support (ACNS0334 protocol), while older children are given radiotherapy and tandem high dose chemotherapy with stem cell support (SJMB03 protocol). We postulate that a resection of the primary tumor is not obligatory, and a biopsy may suffice in order to enable prompt oncological treatment without affecting the long-term survival. PATIENTS AND METHODS Between 2010-2019 7 patients with metastatic medulloblastoma (median age 4.5, age 1–10) were treated with biopsy only, five spinal and two from the primary tumor. Six children had a concurrent VP shunt. Four presented with cord compression, and two with neurological deterioration. Four needed emergency radiotherapy. Two infants received protocol ACNS0334, five patients received protocol SJMB03. RESULTS Six patients (85%) survived; .3 patients are long term survivors (> 5 years), 2 patients are in remission for 2–3 years, one patient is on active therapy. Only 1 patient died after a late (4 years) metastatic relapse not in the posterior fossa. CONCLUSIONS Metastatic medulloblastoma can be cured without excision of the primary tumor and without mutilating surgery. Long term prognosis is probably more attributable to disease subtype and prompt oncologic treatment. This approach merits further studies and may have implications on treatment of non-metastatic tumors.