Lineage Switch Between B-Lymphoblastic Leukemia and Acute Myeloid Leukemia Intermediated by "Occult" Myelodysplastic Neoplasm: Two Cases of Adult Patients With Evidence of Genomic Instability and Clonal Selection by Chemotherapy

Lineage switch in a pediatric patient with KMT2A-MLLT3 from acute megakaryoblastic leukemia to T cell acute lymphoblastic leukemia at the fourth relapse after allo-HSCT: with literature review

We present a patient with acute megakaryoblastic leukemia (AMKL) harboring KMT2A-MLLT3 that converted to T cell acute lymphoblastic leukemia (T-ALL) at her fourth relapse. A 4-year-old girl developed AMKL with multiple swollen lymph nodes. She exhibited several recurrences in the bone marrow and died of septic shock after her fourth relapse. Bone marrow cells at the initial diagnosis and at all four relapses had the same KMT2A-MLLT3 fusion transcript. She also developed a somatic mutation (c.7177C > T p.Q2393X) of NOTCH1 at the fourth relapse. This sequential phenotypic and cytogenetic study may yield valuable insights into the mechanism of AMKL to T-ALL lineage switch and possible implications for treatment selection.

To B- or not to B-: A review of lineage switched acute leukemia

Acute leukemia is a heterogeneous disorder of hematologic malignancies composed primarily of hematopoietic precursors that have acquired unregulated self-renewal and proliferation. Hematology classification systems typically divide these neoplasms into lymphoid (B- or T-) and myeloid-lineage subtypes, with therapy dependent upon this distinction. Infrequently, certain acute leukemias may undergo a complete lineage switch at relapse, subsequently complicating the diagnosis and treatment of these recurrent diseases. Transformation from B-lineage to myeloid lineage is the most common switch observed, and is frequently associated with a balanced 11q23 translocation, involving KMT2A. The mechanisms involved in the lineage-switch are unclear, but modern therapies targeting the B-cell-specific marker, CD19, have proven to promote this conversion as one means of treatment escape. Broadly speaking, therapy-mediated selection of alternate lineage-committed subclones derived from the same initial pluripotent progenitors, clonal evolution and reprogramming of lineage-committed blasts, and de novo clonally unrelated leukemias may account for the clinical impression of lineage switched acute leukemia during treatment. This review will explore the phenomenon and potential mechanisms of lineage transformation during the treatment of acute leukemia.

Repeated Lineage Switches in an Elderly Case of Refractory B-Cell Acute Lymphoblastic Leukemia With MLL Gene Amplification: A Case Report and Literature Review

Lineage switches in acute leukemia occur rarely, and the underlying mechanisms are poorly understood. Herein, we report the case of an elderly patient with leukemia in which the leukemia started as B-cell acute lymphoblastic leukemia (B-ALL) and later changed to B- and T-cell mixed phenotype acute leukemia (MPAL) and acute myeloid leukemia (AML) during consecutive induction chemotherapy treatments. A 65-year-old woman was initially diagnosed with Philadelphia chromosome-negative B-ALL primarily expressing TdT/CD34/HLA-DR; more than 20% of the blasts were positive for CD19/CD20/cytoplasmic CD79a/cytoplasmic CD22/CD13/CD71.The blasts were negative for T-lineage markers and myeloperoxidase (MPO). Induction chemotherapy with the standard regimen for B-ALL resulted in primary induction failure. After the second induction chemotherapy regimen, the blasts were found to be B/T bi-phenotypic with additional expression of cytoplasmic CD3. A single course of clofarabine (the fourth induction chemotherapy regimen) dramatically reduced lymphoid marker levels. However, the myeloid markers (e.g., MPO) eventually showed positivity and the leukemia completely changed its lineage to AML. Despite subsequent intensive chemotherapy regimens designed for AML, the patient’s leukemia was uncontrollable and a new monoblastic population emerged. The patient died approximately 8 months after the initial diagnosis without experiencing stable remission. Several cytogenetic and genetic features were commonly identified in the initial diagnostic B-ALL and in the following AML, suggesting that this case should be classified as lineage switching leukemia rather than multiple simultaneous cancers (i.e., de novo B-ALL and de novo AML, or primary B-ALL and therapy-related myeloid neoplasm). A complex karyotype was persistently observed with a hemi-allelic loss of chromosome 17 (the location of the TP53 tumor suppressor gene). As the leukemia progressed, the karyotype became more complex, with the additional abnormalities. Sequential target sequencing revealed an increased variant allele frequency of TP53 mutation. Fluorescent in situ hybridization (FISH) revealed an increased number of mixed-lineage leukemia (MLL) genes, both before and after lineage conversion. In contrast, FISH revealed negativity for MLL rearrangements, which are well-known abnormalities associated with lineage switching leukemia and MPAL. To our best knowledge, this is the first reported case of acute leukemia presenting with lineage ambiguity and MLL gene amplification.

Lineage Switch in an Infant B-Lymphoblastic Leukemia With t(1;11)(p32;q23); KMT2A/EPS15, Following Blinatumomab Therapy

We report a 6 month-old infant girl with t(1;11)(p32;q23), KMT2A/EPS15-rearranged B-acute lymphoblastic leukemia (B-ALL) that was refractory to traditional ALL-directed chemotherapy. Following administration of blinatumomab, she experienced lineage switch from B-ALL to acute myeloid leukemia (AML). Myeloid-directed chemotherapy resulted in clearance of AML by flow cytometry, though a residual CD19+ B-ALL population persisted (0.14%). Following bridging blinatumomab, the patient achieved B-ALL and AML remission, as measured by flow cytometry. The patient subsequently underwent allogeneic hematopoietic stem cell transplant. Unfortunately, she relapsed with CD19+ B-ALL one-month post-transplantation. Next generation sequencing study of IGH/IGL using ClonoSEQ® analysis detected 3 dominant sequences all present in her original B-ALL, lineage switched AML, and post-transplant relapsed B-ALL, though the latter showed an additional 4 sequences, three of which were present at low abundance in the original diagnostic sample. The presence of the same clones throughout her disease course suggests cellular reprogramming and differentiation following chemotherapy and immunotherapy. This is the first reported case of lineage switch of B-ALL with t(1;11) and also the first report of a lineage switch case that used ClonoSEQ® to define the clonality of the original B-ALL, lineage switched AML, and relapsed B-ALL.

CD3-positive diffuse large B-cell lymphoma relapses as CD3-negative large B-cell lymphoma: Loss of aberrant antigen expression in B-cell lymphoma after chemotherapy

Aberrant expression of CD3 on diffuse large B-cell lymphoma (DLBCL) is rare, and its mechanism and biological significance are currently unclear. Herein we report a case of Epstein-Barr virus-negative, CD3-positive DLBCL in a 53 year-old male, who had a remote history of renal transplantation. After standard chemotherapy, the patient was in clinical remission. He relapsed three years later, but at this time with apparent loss of CD3 expression. PCR-based IGK gene rearrangement studies demonstrated clonal amplicons with an identical nucleotide size between the primary and secondary DLBCL, confirming the clonal relationship despite their phenotypic differences. To our knowledge, this is the first case of CD3-positive DLBCL that demonstrated a loss of aberrant CD3 on relapse. The chronologic change in phenotype seen in this case suggests that the source of the patient's lymphoma relapse may arise from either a quiescent subclone without CD3 expression, or from an upstream neoplastic precursor cell.