Impact of Somatic Mutations on the Outcome of Children and Adolescents with Therapy-Related Myelodysplastic Syndrome

Myelodysplastic syndromes (MDS) following chemo- and/or radiotherapy for primary malignancy in childhood are clinically heterogeneous and generally resistant to therapy. Current knowledge about the clinical course and the underlying genetic background is imprecise with the exception of structural complex karyotype indicating a particular dismal prognosis. Here, we employed a next generation sequencing (NGS) of 28 genes previously established to assess the mutational landscape in primary pediatric MDS. Using Ampliseq PCR enrichment and Miseq NGS we deep sequenced DNA from bone marrow of 80 patients (pts) with therapy-related MDS (t-MDS) included in the registry of the European Working Group of MDS in Childhood (EWOG-MDS). The 41 males and 39 females had been diagnosed of t-MDS at a median age of 13 years (yrs, range 1.2-22) following treatment of hematopoietic malignancy (HM, 44), solid tumor (ST, 22) or brain tumor (BT, 14). The interval from primary malignancy to t-MDS was 3.2 yrs (0.5-18.5). Morphology was compatible with refractory anemia with excess of blast (RAEB, 34), RAEB in transformation (RAEB-t, 9), MDS related acute myeloid leukemia (MDR-AML, 4), chronic myelomonocytic leukemia (CMML, 14) or MDS without increase of blasts (19). Cytogenetic aberrations were seen in 80% of the patients, most frequently monosomy 7 (29%) and a structural complex karyotype (22%) detected in all morphological entities and subgroups of primary malignancy.

Mutations were noted in 50% of pts with 1, 2, 3 or 4 genes affected in 33%, 10%, 6% and 1% respectively. Recurrent mutations were identified in RUNX1 (13.8%), TP53 (12.5%), CBL (8.8%), ASXL1 (7.5%), PTPN11 (7.5%), SETBP1 (5.0%), NRAS (5.0%), KRAS (3.8%), BCORL (2.5%), CSF3R (2.5%), HOXA9 (1.3%), EZH2 (1.3%), PTEN (1.3%), JAK3 (1.3%), STAG2 (1.3%), RAD21(1.3%). No mutations were detected in GATA2, CEBPA, GATA1, BCOR, FLT3, JAK2, cKIT, MPL, CTCF, VPS45, CALR, SH2B3. TP53 mutations arose as an isolated genetic event in the majority of cases (8/10) unlike RUNX1 mutations frequently occurring in combination with other genetic lesions (9/11). According to primary malignancy TP53 mutations were detected in all subgroups (14% HM, 63% ST, 14% BT), whereas RUNX1 mutations were absent in the group with prior solid tumor. Mutations in TP53 were strongly correlated with a structural complex karyotype (9/10). With the exception of MDS without increase of blasts characterized by the absence of RAS pathway alterations, the mutational landscape did not segregate with the morphological subtype. With a median follow-up of 5.3 yrs (0.1-13.7) for pts alive and 68/80 pts treated with hematopoietic stem cell transplantation (HSCT), the probability of overall survival (OS) at 5 yrs was 0.44. OS was worse for patients with more advanced disease (RAEB-t/MDR-AML 0.12 vs CMML 0.29 vs RAEB 0.49 vs MDS without increase of blasts 0.61, p=0.07) and t-MDS following solid tumor (ST 0.30 vs HM 0.49 vs BT 0.46, p=0.09). As expected the detection of a structural complex identified a group with a dismal outcome (OS 0.09 vs 0.37 with normal karyotype vs 0.55 with monosomy 7/ 7q- vs 0.62 with other cytogenetic aberrations, p<0.01). Assessing the impact of mutations on outcome, pts with any mutation had a worse outcome compared to pts with no mutation (OS 0.25 vs 0.60, p<0.01). Mutations in TP53 and RAS pathway were associated with a lower OS of 0.00 and 0.19, respectively, whereas RUNX1 mutated cases without TP53 or RAS pathway alteration had an excellent outcome with 5/5 pts being alive.

This study demonstrates that the outcome of patients with t-MDS is variable and may currently be best defined by the genes mutated. Although the germline status was not tested in all cases with TP53 mutation, the study indicates that presence of somatic TP53 or RAS pathway mutations will help identifying patients that are at high risk of treatment failure and therefore candidates for experimental therapy. At the same token, the majority of t-MDS patients without these high risk mutations can successfully be treated with HSCT. Thus, future counseling of patients with t-MDS and their parents will require individual molecular genotyping.