Interphase FISH Analysis Of Multiple Myeloma Molecular Risk At First Relapse: Results From The BSBMT/Ukmf Myeloma X (Intensive) Trial
Authors: Cook Gordon , Ashcroft John , Williams Cathy D. , Cairns David A , Fletcher Marie , Parrish Christopher , Cavenagh James D. , Snowden John A , O'Connor Sheila J , Owen Roger G , Brown Julia , Morris Treen 
Published: October 2019

Abstract

Introduction
Heterogeneity of molecular abnormalities in myeloma plasma cells (PCs) & their impact on clinical outcomes has been clearly demonstrated in newly diagnosed patients & advanced disease stages. Limited analysis at first relapse stage & in particular the impact of molecular risk categories on intensive re-induction/consolidation therapy limits the use of such analysis to predict suitable patient selection.

Patients and Methods
MM patients relapsing >18 months after a prior ASCT were enrolled into a phase III RCT, receiving a Bortezomib-containing regimen (Bortezomib, Doxorubicin and Dexamethasone) before being randomised to either a second ASCT or Cyclophosphamide weekly. BM aspirate samples at trial entry and at further disease progression were CD138 positively selected (Miltenyi AutoMac) and PC suspensions were fixed in Carnoy’s then stored at -20°C. Interphase FISH analysis (iFISH), was performed with commercial probes, scored and image captured (Zeiss AxioPlan microscopy with MetaSystems software). Depth of response (IMWG criteria) was analysed post-induction and 100 days post-randomisation with durability of response determined as time-to-progression (TTP).

Results
222 samples from 297 patients were received & satisfactory CD138+ cell purity and yield was obtained in 149 samples (68% recovery). Of these, only 35 (28%) demonstrated no genetic defects by iFISH at trial entry. A single genetic abnormality was detected in 28 patients (23%): del13q (n=8), IGH rearrangement (n=16), MYC rearrangements (n=2) and del17p (n=2). 2 and ≥3 molecular genetic abnormalities defects were detected in 42 patients (28%) and 32 patients (21%), respectively. The commonest abnormality detected was an IGH rearrangement (n=62, 41%) & there were insufficient CD138+ cells for additional translocation testing in 11/62; Of the 51 IGH rearranged samples, a partner translocation was identified in 32 (63%): CCND1/IGH in n=15 (29%), FGFR3/IGH in n=14 (27%) and IGH/MAF in n=3 (6%) with an additional single genetic defect detected in 31 samples (50%). Del13q was present in 58 patients (39%) of whom 29 patients (50%) demonstrated one additional genetic defect (IGH rearrangement n=22, del17p n=3 and MYC rearrangements n=4), 20 patients (35%) demonstrated 2 additional defects and 2 patients demonstrated >2 additional defects. A rearranged MYC was detected in PCs from 24 patients (16%) with 2 & ≥3 additional defects detected in 13 & 6 patients’ samples, respectively. Del17p was detected in PCs from 22 patients’ samples (15%) with additional copies of Ch17 present in PCs of 8 patients (6%). All Ch17+ patient samples exhibited additional genetic defects. Where del17p clones were detected, 9 and 10 samples had 1 & ≥2 genetic defects. When del17p was present, MYC arrangements were also detected in 16 patients (73%). 20 patients (13%) demonstrated hyperdiploidy with 8 patients demonstrating no other defect. The presence of IGH and MYC rearrangements or del17p did not correlate with the duration of response from ASCT1 nor did it impact the ORR or sCR to bortezomib-based induction. The presence of IGH and MYC rearrangements or del17p did not impact on the TTP in the C-weekly cohort, however both del17p (median TTP - absent: 19 mns, 95%CI, 16-25 mns, vs. present: 10 mns, 95%CI, 2-11 mns; logrank p=0.002) and MYC rearrangements (median TTP absent: 24 mns, 95%CI 12-42 mns vs. present: 11 mns, 95%CI 1-18 mns; logrank p=0.006) impacted on TTP in the ASCT2 cohort. Only the presence of MYC rearrangements were predictive of reduced TTP in the ASCT2 group (Cox regression model interaction test HR 0.08, 95%CI 0.02-0.44; p=0.003) when accounting for treatment response to previous ASCT & response to induction therapy.

Conclusion:
IGH rearrangements were identified at a similar frequently to analyses reported at presentation though with disproportionately more FGFR3/IGH and MAF/IGH abnormalities. Otherwise, the incidence of genetic abnormalities was similar to rates reported at diagnostic with a frequent association of MYC rearrangements with del17p. Whilst both del17p and MYC rearrangements were associated with inferior durability of response following an ASCT, only a MYC rearrangement was of independent predictive significance. As follow-up is limited, the impact on overall survival currently remains to be determined.

Disclosures:
Williams: Janssen: Honoraria, Speakers Bureau. Snowden:Janssen: Honoraria, Research Funding, Speakers Bureau.