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Plasma cell-free DNA chromosomal instability score as early predictor to monitor tumor burden in response to therapeutic in multiple myeloma patients.

8036 Background: Multiple myeloma (MM) is a plasma cell malignancy characterized by chromosomal instabilities (CIN). Here we investigate the potential of cell-free DNA CIN as non-invasive biomarker to predict early response for MM treatments. Methods: In this prospective study, we recruited 11 relapsed/refractory (RRMM) and 19 newly diagnosed (NDMM) patients at Changzheng Hospital. Plasma samples were collected after finished two cycles or one month (RRMM) of therapy, with matched ones before the current regimen. cfDNA was extracted, followed by CIN analyses by using a customized bioinformatics workflow, ultrasensitive chromosomal aneuploidy detector (UCAD). Criteria for response and progression were according to the IMWG (Durie BG et al. 2006). Results: 7 (23%) patients (5 RRMM and 2 NDMM) showed high cfDNA CIN regard as strong positive after two cycles of treatment. Plasma cfDNA CIN profiling found complex clonal evolution compared two cycles to baseline. Multiple genomic regions, including chr7, 17p (TP53), 12q and 3p, were involved in clonal evolution. The degree of cfDNA CIN correlated with myeloma stage and overall survival. Remarkably, of the 5 heavily treated RRMM patients and 1 primary refractory newly diagnosed patient, 3 died within 60 days after the last time of cfDNA detection. Nine patients (30%) of patients showed positive cfDNA CIN after two cycles of treatment, which response rate was 11% (n=1) with SD, 33% (n=3) with MR, and 56% with PR, respectively. Fourteen patients with 5 RRMM and 9 NDMM were detected marginal or negative cfDNA CIN after two cycle’s treatment. The overall response rate in 14 patients was 100%, including 14.3% with a complete response, 14.3% with a very good partial response (VGPR), 57.1% with a PR, and 14.3% with a MR. Of these patients, 3 RRMM who received with more than six lines of therapy, showed positive cfDNA CIN. Subsequently, these three heavily treated RRMM patients have chance to enroll the chimeric antigen receptor T-Cell immunotherapy (CAR-T) therapy (enrolled NCT03093168). Surprisedly, all of them benefit from the CAR-T therapy to improve responses dramatically, meanwhile, the dynamics of total cfDNA concentration correlated with tumor burden to negative. Conclusions: We provide evidence that cfDNA level correlates with tumor burden and response rate in MM. For heavily pre-treated advanced RRMM patients with cfDNA CIN positive were benefit from the CAR-T therapy. Therefore, serial plasma cfDNA analysis is a robust and sensitive tool for monitoring response to therapy.