Blood Cancer ( Leukemia) -its types , causes , symptoms, diagnosis.

Leuk- refers to white blood cells, and -emia refers to the blood, so in leukemia , there’s uncontrolled proliferation of partially developed white blood cells, also called blast cells, which build up in the blood over a short period of time. Although leukemia means cancer white blood cells, it can also be used to refer to cancer of any of the blood cells, including red blood cells and platelets. 

Acute leukemia can be broadly classified into acute myeloid leukemia, or AML; and acute lympho blastic leukemia, ALL. AML is more common in old age, where as ALL is more common in children. In both cases, accumulation of blast cells interferes with the development and function of healthy white blood cells, platelets, and red blood cells. 

Now, every blood cell starts its life in the bone marrow as a hematopoietic stem cell. Hematopoietic stem cells are multi potent -- meaning that they will produce to both myeloblasts, which are precursors of myeloid blood cells,and lymphoblasts, which are precursors of lymphoid blood cells. These lymphoblasts can be pre-B cells, whichdevelop into B lymphocytes; or pre-T cells, which develop into T lymphocytes. If a hematopoietic stem cell develops into a myeloid cell, it’ll mature into an erythrocyte -- or a red blood cell, a thrombocyte -- ora platelet, or a leukocyte -- or a white blood corpuscle , sort of a monocyte or granulocyte. Granulocytes are cells with tiny granules inside of them -- they include neutrophils, basophils, and eosinophils. If a hematopoietic stem cell develops into a lymphoid cell, on the other hand, it’ll mature into some other kind of leukocyte:a T cell, a B cell, or a natural killer cell, which are referred to as lymphocytes. Once the varied blood cells form, they leave the bone marrow, and travel round the blood, or calm down in tissues and organs like the lymph nodes and spleen.

Acute leukemia is caused by a mutation in the precursor blood cells in the bone marrow. In the case of ALL it’s usually due to a chromosomal translocation or due to an abnormal chromosome number. Common chromosomal trans locations include translocation of chromosome 12 and 21 and translocation of chromosome 9 and 22, also called the Philadelphia chromosome. These result in production of abnormal intracellular proteins, which affect the cell’s function and cell division. ALL can further be classified into T-cell ALL, where there’s proliferation of T-cell precursors, and B-cell ALL, where there’s proliferation of B-cell precursors. AML is caused by a wide variety of abnormalities like chromosomal trans locations, which are used to sub classify AML into a few different types.

 AML can also be classified based on the morphology of the myeloblast into AML without maturation; AML with minimal maturation, AML with maturation;acute promyelocytic leukemia; acute myelomonocytic leukemia, acute monocytic leukemia, acute erythroid leukemia, and acute megakaryoblastic leukemia. Of these, acute promyelocytic leukemia isan important sub type. It is characterized by translocation of chromosome15 and 17 which disrupts the retinoic acid receptor alpha gene, which is required for normal cell division. Now, there are also certain conditions that can actually lead to AML, like myelodysplastic syndrome, which is characterized by defective maturation of myeloid cells and buildup of blasts in the bone marrow. Usually the buildup is initially less than 20% blasts. But that’s enough to cause a decrease in the function of red blood cells, granulocytes, and platelets. As the disease progresses, the blast percentage may go over 20%, resulting in AML with a background of myelodysplasia. Another condition often associated with both AML and ALL is Down syndrome, which is caused by an extra 21st chromosome - so that there’s a trisomy 21.

Finally, there also are some risk factors for leukemia like exposure to radiation, and alkylating chemotherapy, which can have been used as treatment of another sort of cancer. Alright, now no matter the sort of mutation,acute leukemias share an identical pathogenesis. The mutation does two things. First, it causes these precursor blood cells to lose their ability to differentiate into mature blood cells. This means that they’re stuck in the blast stage of development, and the blast cells don’t function effectively. Second, it makes the blast cells divide uncontrollably,and within the process take up tons of space and nutrition within the bone marrow. This means that the other normal blood cells growing in the bone marrow get “crowded out”, and it’s tough for them to survive with the extra competition for nutrients. This causes cytopenias, or a discount in the number of healthy blood cells, like anemia, which may be a reduction of healthy red blood cells, thrombocytopenia, a discount of healthy platelets, and leukopenia, or a reduction of healthy leukocytes. As the number of blast cells in the bone marrow keep increasing, they spill out into the blood.

Now some of these , especially lympho blasts,settle down in organs and tissues across the body, like the liver and spleen. Sometimes, pre- T cells, in T- cell ALL migrate to the thymus or lymph nodes like normal T-cells do, and settle down there, causing these structures to enlarge.

Also, in acute promyelocytic leukemia, the promyelocytes activate the clotting process, and this combined with the already decreased platelets, results in disseminated intravascular coagulation.

Symptoms

symptoms of both AML and ALL include fatigue,because of the anemia, easier bleeding, because of the thrombocytopenia, and more frequent infections, because of the leukopenia. Pain and tenderness in the bones can occur when there’s increased cell production which causes the bone marrow to expand. Hepatosplenomegaly often causes a feeling of abdominal fullness, while the lymphadenopathy often causes mild, but localized pain in the lymph nodes. However, hepatosplenomegaly and lymph adenopathy are both seen more prominent in ALL than in AML. In addition, monocytic variety of AML causes swelling of gums because of monocytic infiltration. Thymus enlargement in T-ALL may present as a mass, or growth in the media stinum. The diagnosis of AML and ALL usually starts with a peripheral blood smear, which shows a lot of blast cells, myeloblasts in case of AML, and lymphoblasts in case of ALL.