Molecular Genetics Provides Important Information for Initial Evaluation of Patients with Suspected MDS

Background: Myelodysplastic syndromes(MDS) are clonal disorders of hematopoiesis characterized by peripheral blood cytopenia, dysplasia in one or more myeloid cell lineages and increased risk for transformation to AML. Diagnosis of MDS according to the current WHO classification requires cytomorphology and cytogenetics for detection of blasts, dysplasia and/or MDS-specific cytogenetic abnormalities. Diagnosing or excluding MDS may be challenging in cases with inconclusive cytomorphology and/or absence of cytogenetic alterations. A recent study (Malcovati et al ., Blood 2017) implicates that mutation analysis may significantly improve the current diagnostic workup in patients with unexplained cytopenia, also described as idiopathic cytopenia of undetermined significance (ICUS), and allow estimation of risk of hematologic malignancies.

Aims: 1) Evaluating the yield of information on mutations (mut) in patients with ICUS. 2) Estimate the predictive impact of these findings.

Methods: To retrospectively analyze the molecular mutation pattern of ICUS patients (pts), we defined a cohort of 51 consecutive pts sent to our institution between August 2005 and December 2016 according to the following criteria: 1) ICUS defined according to Steensma et al ., Blood 2015, availability of 2) peripheral blood counts and 3) sample material sufficient for molecular analysis and 4) cytomorphologic reevaluation of bone marrow after a minimal follow up period of 6 months (median: 20 months; range: 6-103 months). The cohort consisted of 33 males and 18 females, median age was 69 years (y) (range: 27-80 y).

Targeted sequencing of 38 genes commonly mutated in myeloid malignancies was performed in all 51 pts (Illumina, San Diego, CA). Data was analyzed by SeqNext 4.3 software (JSI Medical Systems, Kippenheim, Germany).

Results: 24/51 pts with ICUS at diagnosis (47%) were cytomorphologically diagnosed with myeloid neoplasms (MN) at follow up evaluation (7/24 pts AML, 15/24 pts MDS and 2/24 pts MPN). At initial evaluation, 22/51 ICUS pts (42%) carried a somatic mut in at least one of the genes analyzed (range: 1-5) and were thus reclassified as clonal cytopenias of undetermined significance (CCUS). The most frequently mutated genes were TET2 (36% of all mut), ASXL1 (27%), SRSF2 (27%), SF3B1 (23%), RUNX1 (18%), DNMT3A (18%)and ZRSR2 (18%) .

According to the newly proposed risk stratification by Malcovati et al., 18/22 pts with CCUS (82%) showed a mutation pattern associated with a high risk to develop a MN (spliceosome gene mutations or mutations in TET2, ASXL1 or DNMT3A in combination with additional mut). 4/22 CCUS pts (18%) presented a low risk mutation pattern (3/4 pts with sole DNMT3A mut, 1/4 pts with sole TET2 mut). Cases with high risk CCUS had a non-significantly higher mean variant allele frequency compared to low risk CCUS pts (37% vs. 25%).

Notably, all pts who developed AML or MPN in clinical course, had at least one mutation at the time-point of initial evaluation and all these pts had a high risk mutation profile.

In the total cohort of 51 pts the Kaplan-Meier estimate of probability of MN was 32% at 2 y. Probability of MN at 2 y was significantly higher in pts initially diagnosed as CCUS compared to ICUS pts (49% vs. 19%; p= 0.011). However, there was no significant difference of MN probability in high risk CCUS vs. low risk CCUS pts (49% vs. 50%), which may be due to small case numbers. Focusing on the prognostic relevance of individual genes, we found a significantly higher probability of MN at 2 y for patients carrying mut in ASXL1 (83% vs. 22%; p< 0.001), RUNX1 (57% vs. 22%; p= 0.014) and SRSF2 (75% vs. 22%; p= 0.001) compared to pts with unmutated status of these genes. Analyzing ASXL1, RUNX1 and SRSF2 in combination revealed that a mutated status in at least one of these genes significantly increased the probability of MN at 2 y (61% vs. 25%; p=0.003). Carrying mutations in the genes SF3B1 or ZRSR2 did not impact on the probability of MN at 2 y.

Summary: Our study further supports the diagnostic value of molecular genetic testing at the time of initial evaluation of patients with unexplained cytopenias. Mutation analysis identifies clonal disease, which is of clinical importance, as patients carrying somatic mutations have significantly increased risk of developing MN. Furthermore, our data suggests that mutations in specific genes, i.e. ASXL1, RUNX1 and SRSF2, may be particularly relevant for the risk of MN in CCUS patients.