Around 803 new cases of Acute Lymphoblastic Leukemia (ALL) are diagnosed in the United Kingdom every year (Cancer Research UK, 2018). Cytarabine (Ara-C) is a chemotherapeutic drug used to treat leukemic patients, however, chemotherapy resistance occurs frequently. Mechanisms of chemotherapy resistance to Ara-C are poorly understood. DNA mismatch repair (MMR) pathway is one of the pathways responsible to repair errors caused during DNA replication. MMR can also repair damage due to Ara-C and therefore a proficient MMR can confer resistance to Ara-C. Our project aims to investigate the expression of MMR genes MSH2 and MSH3 in ALL carrying Mixed Lineage Leukemia (MLL), also known as KMT2A, chromosomal translocations.