Acute Leukemia and the FLT3 Receptor By: Betty Sa’ Mentor: Dr. Govind Bhagat Site: Columbia University Vanderbilt Clinic

Leukemia is a cancer of the blood in which immature hematopoietic cells proliferate in an uncontrolled manner. Leukemia originates in the bone marrow and quickly spreads elsewhere. There are four major types of Leukemia, Acute Myeloid Leukemia (AML), Acute Lymphoblastic Leukemia (ALL), Chronic Myeloid Leukemia, and Chronic Lymphocytic Leukemia. But we are only focusing on AML and ALL. Acute: means that the disease appears quickly and advances rapidly, so patients with ALL and AML usually require immediate treatment.

Acute Lymphocytic Leukemia (ALL) is a rapidly progressing disease marked by the overabundance of immature lymphoid cells called lymphoblasts (fight bacterial and viral infections) in the blood or bone marrow; most commonly found in children. (explain) Acute Myeloid Leukemia (AML) is a rapidly progressing cancer in which there is uncontrollable growth of immature myeloid cells, caused by some type of mutation (myeloblasts, promyelocytes, monoblasts, erythroblasts, megakaryoblasts) in the bone marrow that leads to a deficiency of red blood cells, platelets, and white blood cells. (explain)

*Since there are many different types of myeloid cells there are also may different subtypes of AML depending upon exactly which type of cell has become leukemic the stage of maturation the cells are at and whether the cells are differentiated, these sub-types include: Acute Myeloid Leukemia without maturation, Acute Myeloid Leukemia with maturation, Acute Promyelocytic Leukemia (APL), Acute Myelomonocytic Leukemia, Acute Monocytic/ Monoblastic Leukemia, Acute Erythroleukemia, and Acute Megakaryoblastic Leukemia).

AML ALL

FLT3 or FMS-like tyrosine kinase 3, is a gene that encodes a membrane-bound receptor tyrosine kinase (RTK), which plays a crucial role in normal haematopoiesis. Normally, FLT3 expression is restricted to CD34+ hematopoietic stem cells, brain, placenta, and gonads. FLT3 is normally activated by the FLT3-Ligand which promotes the normal in vitro growth of early stem cells. In Acute Leukemia, mutations of the FLT3 gene have been found to be one of the most common acquired genetic lesions. FLT3 mutations can be detected in about 7-15% of ALL patients and 30% of AML patients.

There are two frequent types of somatic FLT3 genetic mutations: – Internal Tandem Duplications (ITDs) in the Juxtamembrane (JM) Domain (explain) – Point Mutations in the activation loop of the Tyrosine Kinase Domain (TKD). (explain) The presence of FLT3/ITD mutations is associated with a poor clinical outcome in both pediatric and adult patients with ALL and AML. But TKD mutations, unlike ITD mutations, have not been shown to have any prognostic significance in ALL or AML patients. The presence of FLT3/ITD mutations is associated with a poor clinical outcome in both pediatric and adult patients with ALL and AML. But TKD mutations, unlike ITD mutations, have not been shown to have any prognostic significance in ALL or AML patients. Both types of FLT3 mutation cause ligand-independent activation of the receptor and activation of downstream signaling pathways.(explain) Both types of FLT3 mutation cause ligand-independent activation of the receptor and activation of downstream signaling pathways.(explain)

In 2006 an estimated 3,930 adults (2,150 men and 1,780 women) in the US will be diagnosed with ALL and an estimated 1,490 (900 men, 590 women) deaths will occur. ALL is more common in adults older than % to 30% of adults with ALL experience long-term disease remission or are cured of the disease. ALL is more common in children than in adults; 74% of all new cases are diagnosed in children ages 0 to 19. In 2006, an estimated 11,930 people (6,350 men and 5,580 women) in the US will be diagnosed with AML and an estimated 9,040 deaths will occur (5,090 men and 3,950 women). AML is most common in older adults around years old. The percentage of patients who survived at least five years after being diagnosed, for adults under the age 65 with AML is 33%. The percentage of patients who survived at least five years after being diagnosed, for adults under the age 65 with AML is 33%.

To get a better understanding of the molecular abnormalities underlying Acute Leukemia's. I will study the different types of FLT 3 tyrosine kinase mutations in subsets of acute leukemias to determine their relative frequency and impact on the biologic course of disease. I will also correlate the presence of FLT3 mutations with other cytogenetic abnormalities in different types of acute leukemias to better understand the multi-step pathways of leukemogenesis.

Case selection: Acute leukemias diagnosed at Columbia University Medical Center over the past 5 years for which cytogenetic information is available (at least 100 cases) DNA extraction from peripheral blood or bone marrow aspirate samples PCR using primers specific for Exons 11and 12 of the FLT3 gene Capillary gel electrophoresis Analysis of electropherograms for FLT3-ITD mutations (Direct electrophoresis) and FLT3/TKD mutations (restriction enzyme digestion followed by electrophoresis).

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Dr. Govind Bhagat Dr. Govind Bhagat Dr. Mahesh Mansukhani Dr. Mahesh Mansukhani Columbia University Dr. Sat Dr. SatMSKCC Harlem Children Society Harlem Children Society