Impact of Clonal Heterogeneity in Newly Diagnosed, Transplant-Eligible Multiple Myeloma – Subgroup Analysis of the GMMG HD6 Phase III Trial

Introduction

Multiple myeloma (MM) is a heterogeneous disease with survival ranging from months to decades based on a patient’s risk profile. Clonal heterogeneity is considered one of the major drivers of disease evolution towards an aggressive phenotype and therapy resistance. In the current study, we investigated the prognostic impact of clonal heterogeneity identified by fluorescence in situ hybridization (FISH) in a large cohort of newly diagnosed, transplant-eligible MM patients treated within the prospective GMMG HD6 trial (Mai et al., Lancet Hematol, 2024).

Methods

The GMMG-HD6 trial phase 3 randomized study was conducted at 69 sites across Germany. Patients aged 18–70 with untreated, symptomatic MM were randomly assigned to one of four treatment groups: Induction therapy included either four 21-day cycles of RVd (lenalidomide, bortezomib, dexamethasone) or RVd plus elotuzumab (E-RVd). Following autologous stem-cell transplantation, patients received either RVd or E-RVd consolidation and maintenance with R or E-R for 2 years, respectively. Since the trial showed no significant differences in progression-free survival (PFS) between the four arms, patients were pooled for the current analysis. Subclones at a chromosomal location were detected if the largest abnormality was present in at least 60% of cells and the subclone abnormality was present in at least 10% of cells, had at least 30% less cells than the largest abnormality and was present in maximally 2/3 of the largest abnormality (Merz et al., Blood advances, 2017). The GMMG HD 6 trial is registered at ClinicalTrials.gov (NCT02495922) and is completed.

Results

Between 06/2015 and 09/2017, 564 patients were enrolled. After a median follow-up of 49.8 months, there was no significant difference in PFS among the four treatment groups, with 3-year PFS rates ranging from 66-69%, respectively. Complete FISH data were available in 478 patients. IgH translocations occurred primarily as main clonal events with only ten patients harboring subclonal IgH translocations. Secondary events like deletions of chromosomes 1p12 (n=32/8%), 8p21 (n=49/11%), 13q14 (n=48/10%) and 16q23 (n=36/8%) were the most frequently detected subclones followed by gains of chromosomes associated with a hyperdiploid (HD) karyotype, ranging from 3% (n=12 for gain 19q13) to 6% (n=26 for gain 9q34). High-risk aberration gain 1q21 was detected in 139 patients (29%) as main clonal event and 45 patients (9%) only in subclones. Deletion 17p13 occurred in 33 patients (7%) as main clone and 26 patients (6%) as subclone. Patients with cytogenetically defined high-risk disease harbored more frequently subclones (59%) compared to standard risk patients 38% (odds ratio 2.3, 95% confidence interval, CI 1.6-3.5, p<0.001). While the general presence of subclones was not associated with inferior PFS or overall survival (OS), significant differences were found for prognostic relevant individual chromosomal lesions: Gain 1q21 was only associated with inferior PFS (hazard ratio, HR, 2.0; 95% CI 1.5-2.7) and OS (HR, 2.5; 95% CI 1.5-4.1, p<0.001, respectively), if detected as main clone, but not as subclonal aberration. Gains of chromosomes connected to a HD karyotype were only linked to improved OS, if present as the main clone (gain 9q34, HR 0.5, 95% CI 0.3-0,9; p=0.017; gain 11 HR 0.5, 95% CI 0.3-0.9; p=0.022). While only subclonal deletions of chromosome 14q were associated with adverse PFS (HR 3.9, 95% CI 1.6-9.5; p<0.001) and OS (HR 8.4, 95% CI 3.0-23.1; p<0.001), the negative prognostic implications of del17p were persistent regardless whether detected as main or subclonal aberration.

Conclusion

Not only the mere presence or absence of chromosomal aberrations, but also their clonal hierarchy needs to be accounted for when assigning risk based on genetic lesions.