Acute Monoblastic Leukemia and Myeloproliferative Neoplasm Observed in an Elderly Man Had the Same Clonal Origin

It is reported that fonder mutations affects the development these disorders closely. However, it is unclear whether hematopoiesis carrying these mutations could contribute to the development of the different diseases, directly. We here report a case of acute monoblastic leukemia (AMoL) followed by myeloproliferative neoplasm, unclassifiable (MPN-U), 2 years later, both derived from the same clonal hematopoiesis. [Case report and Methods] A 75-year-old male was admitted to our hospital duo to fever and fatigue. WBC count was 114.7 x 10⁹/L with 9% blasts and 82% monocytes. Bone marrow aspiration revealed 93% of blasts and promonocytes, which resulted in the diagnosis of AMoL with normal karyotype. He received three courses of chemotherapy, which brought CR, but minor monocytosis (>1 x 10⁹/L) persisted without proliferation of immature blasts. After 2 years from the diagnosis of AMoL, platelet count started to increase. WBC count was between 10 and 20 x 10⁹/L without blast, and platelet count reached 500 x 10⁹/L. Bone marrow examination (2 years from the diagnosis of AMoL) revealed normal cellularity, and less than 5% of blast with normal karyotype. Considering the leukocytosis and thrombocytosis, we evaluated his status as similar to MPN, since dysplasia was not apparent on his hematopoietic cells. Although he had previously received chemotherapy for AMoL, it was diagnosed as MPN-U. Two years after the diagnosis of MPN-U, the disease transformed into AML, not AMoL. He died of AML, four years after AMoL developed. To study clonal status of AMoL and MPN-U in this case, bone marrow mononuclear cells of AMoL (at diagnosis) and MPN-U phases, and buccal swab collected during MPN-U phase were subjected to whole exome sequencing (WES). Validation of mutations was performed by amplicon-base deep sequencing. DNA obtained from bone marrow smear during CR was tested whether mutations existed or not by deep sequencing. Mean depth of WES was 89.15, 140.18, and 98.02 for AMoL, MPN-U, and buccal mucosa samples, respectively. Clonal evolution analysis was performed using clonality inference in tumors using phylogeny. [Results] We found total 22 mutations in samples of AMoL and MPN-U phase with different variant allele frequency (VAF) by WES. When AMoL was diagnosed, 16 genes were mutated with more than 10% of VAF, including genes such as ASXL1, CBL, GATA2, NPM1 (4 bp insertion), SRSF2, and TET2. On the other hand, when MPN-U was diagnosed, there were 16 genes mutated with more than 10% of VAF, and 10 mutations out of 16 were the same mutation as found in the sample of AMoL phase including mutations in SRSF2, GATA2, and TET2. Six mutated genes found only in the sample of MPN-U phase included GNAS and JAK2 (V617F mutation). Since 10 out of 22 genes were commonly mutated in both the AMoL and MPN-U samples, we next analyzed the mutational status of these 22 genes in the CR sample using deep sequencing. It was found that the commonly mutated 10 genes in both AMoL and MPN-U were also mutated in the CR sample with high VAF (> 25%). Some gene mutations found only in AMoL, and some only in MPN-U were also present during CR phase but with low VAF (< 10%). Clonal evolution pathway generated by using deep sequence data suggested that before AMoL, there was a founder clone with mutations of TET2, SRSF2, and GATA2, although we could not analyze the sample before AMoL. Mutations in NPM1, ASXL1, CBL, and ASH1L seemed to contribute to the development of AMoL from the founder clone, and those of JAK2 and GNAS for MPN-U. It is also suggested that small amount of hematopoietic stem / progenitor cells containing the JAK2 mutation already existed in CR sample, and these developed into MPN-U probably with gaining other gene mutations. Our data prospectively showed that clonal hematological disorder would arise from a pre-malignant, clonal hematopoiesis that produced normal levels of mature hematopoietic cells. Our analysis clearly demonstrated that two different clonal hematological disorders developed from the same clonal hematopoiesis that had TET2, SRSF2, and GATA2 mutation, which were previously reported as driver mutations. To our knowledge, this is the first report to analyze the progression of AML and MPN from the identical hematopoietic stem cells by WES and deep sequencing validation to model clonal evolution and a case to give a new suggestion about the development of the myeloid malignancies.