Synchronous Dual Hematologic Neoplasms of Myeloid and Lymphoid Lineage Are of Common Clonal Origin

The incidence of synchronous dual hematologic neoplasms (SDHN) of myeloid (M) and lymphoid (L) lineage has long been recognized as higher than would be predicted based on the incidence of each respective disease alone. While the exact pathobiology remains unknown, explanations include a permissive microenvironment, synergistic selection, and/or a shared clonal origin. The latter hypothesis is supported by presence of specific pathogenic variants in both M and L HNs, with diverse, and sometimes discordant prognostic and therapeutic implications [e.g., SF3B1 in myelodysplastic syndrome (MDS) and chronic lymphocytic leukemia (CLL)]. To determine whether SDHNs share a common clonal origin, have distinct clinical outcomes, and should be considered a unique disease entity, we employed several clinical and advanced molecular approaches.

First, we identified SDHN cases with MDS and concomitant multiple myeloma (MM) or CLL and compared clinical outcomes and genetic features to cases with MDS alone. Despite no difference in MDS risk stratification by revised international prognostic scoring system, patients with SDHN (n=37) had significantly worse overall survival (24.2 vs. 39.6 months; p=0.005) than isolated MDS (n=2434). Interestingly, rate of transformation to acute myeloid leukemia (AML) was lower in SDHN group (12.9% vs. 31.8%; p=0.02). We additionally noted a significant enrichment for TP53 (46% vs. 20%; p<0.001), ASXL1 (35% vs. 21%; p=0.03), and SF3B1 (31% vs. 17%; p=0.02) mutations in SDHN-MDS compared to isolated MDS, suggesting that SDHN is characterized by distinct clinical and molecular features.

Next, we sought to determine whether SDHNs are of common clonal origin, utilizing a single-cell DNA-sequencing (scDNA-seq) and surface proteome-based multi-omic assessment on 16 cryopreserved mononuclear cell samples from 14 unique patients with SDHN. This enabled us to evaluate mutations in the above genes enriched in SDHN plus 42 other recurrently mutated genes within cellular subsets defined by immunophenotypes (IPT). These SDHNs had MDS (n=8), chronic myelomonocytic leukemia (CMML) (n=1), AML (n=3), or myelofibrosis (n=2) as their M-HN, and CLL (n=7), MM (n=6), or lymphoplasmacytic lymphoma (n=1) as their L-HN. Two SDHN cases (MDS+MM and AML+CLL) had sequential samples pre- and post-treatment. The Mosaic package was used to delineate surface protein-defined clusters that were projected in UMAP space and cell types were assigned based on manually curated IPT in a patient specific manner. Bone marrow morphology and flow cytometry data from the scDNAseq timepoint were used to corroborate the relative proportions and IPT of M and L malignant subpopulations.

Using this approach, we observed that the scDNA-seq defined dominant clone was invariably composed of M, L, and hematopoietic stem and progenitor cell (HSPC) compartments. For example, in a sample with pathologically defined CMML and MM, the dominant TET2 double-mutant clone was present in 53% of M cells, 26% of L cells, and 13% of HSPCs. In another sample of MDS and CLL, the dominant clone driven by TP53 loss of heterozygosity was distributed equitably among M (26%), L (21%), and HSPC (28%) populations. On analysis of sequential samples of a TP53-mutated SDHN (AML+CLL), the dominant clone remained present in M and L subpopulations at both pre- and post-treatment timepoints. Overall, the median dominant clone lineage composition was 40% (IQR 15%-60%) of M cells, 18% (IQR 10%-34%) of L cells, and 30% (IQR 13%-57%) of HSPCs, compared to 7% (IQR 2%-13%) of T-cells, suggesting a common clonal origin for SDHNs. Whole exome sequencing of flow cytometry-sorted M, L, and HSPC subpopulations in select SDHN samples is ongoing to validate our findings, and results will be presented at the meeting.

Finally, we explored similarities between SDHN and mixed phenotype acute leukemia (MPAL) which is defined by shared expression of M and L markers in neoplasms with ≥20% blasts. Interestingly, we observed aberrant expression of L markers on M cells and M markers on L cells in sc analysis of SDHN. Moreover, there was statistically significant correlation (r=0.75; p=0.01) between myeloblast % and degree of IPT sharing, suggesting that SDHN parallels many features of MPAL. Collectively, our findings suggest that SDHNs have distinct outcomes and are of common clonal origin. Future studies should confirm these findings and consider SDHN as a single disease entity.