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  • Despite advances in medicine,

  • cancer remains one of the most frightening diagnoses patients can receive.

  • What makes it so difficult to cure is that it's not one illness,

  • but a family of over 100 diseases occurring in different types of cells.

  • And one type of cancer has the unfortunate distinction

  • of afflicting children more than any other type.

  • This is leukemia,

  • a cancer that begins in stem cells found in the bone marrow.

  • A stem cell is a bit like an infant,

  • undeveloped but possessing great potential.

  • Many stem cells specialize and become cells of organs,

  • like the liver, brain and heart.

  • But in some tissues,

  • they can continue to divide into new stem cells throughout development,

  • and into adulthood in order to frequently generate new cells

  • and keep up with the body's needs.

  • One example is the bone marrow,

  • where stem cells differentiate into many types of blood cells.

  • That includes red blood cells,

  • which carry oxygen from the lungs to all tissues,

  • platelets, which help stop bleeding by sticking to damaged blood vessels,

  • and white blood cells,

  • which patrol the body, destroying potentially harmful invaders.

  • Every once in a while,

  • something goes wrong during a stem cell's specialization process

  • and harmful mutations occur in the cell's DNA.

  • Cells with compromised DNA are supposed to self-destruct,

  • but some damaged cells ignore this order,

  • replicating uncontrollably, even as they lose their original function.

  • These are what we know as cancer cells.

  • It is not yet clear why leukemia is the most common childhood cancer,

  • but one contributing factor may be

  • that leukemias are often caused by just one or two DNA modifications,

  • while most cancers require many of them,

  • allowing leukemias to arise faster than other types of cancer.

  • Moreover, some DNA alterations can occur in white blood cells

  • during fetal development,

  • further increasing the risk of early leukemia.

  • But though it affects more children than any other cancer,

  • adults constitute the majority of leukemia patients overall.

  • Once leukemia strikes, the damaged cells reproduce in the blood and the bone marrow

  • until they take up all available space and resources.

  • When the bone marrow can no longer produce

  • the required amount of functional cells,

  • the blood becomes depleted.

  • The lack of red blood cells

  • means that muscles don't get enough oxygen,

  • the reduced number of platelets is not sufficient to repair wounds,

  • and the dearth of functional white blood cells impairs the immune system,

  • increasing the risk of infections.

  • To restore the normal function of the blood,

  • leukemic cells have to be eliminated.

  • But because leukemias are not solid tumors,

  • they can't be removed surgically.

  • Instead, the cells are killed inside the body using various treatments

  • that include chemotherapy,

  • a combination of drugs that destroys quickly multiplying cells.

  • Unfortunately, this has the side effect of killing healthy cells,

  • such as those found in hair follicles or intestines.

  • And in some cases, the dosage required is so high

  • that it kills all cells in the bone marrow,

  • including stem cells.

  • When this happens, the body is no longer able to create new blood cells on its own.

  • Fortunately, outside help can come in the form of stem cells

  • from the bone marrow of a donor.

  • Once transplanted into the patient,

  • they rapidly repopulate the bone marrow and the blood.

  • However, bone marrow transplants are a complicated process

  • requiring antigen compatibility between the donor and recipient

  • to keep the transplanted cells from attacking the patient's own cells

  • as foreign bodies.

  • Unlike with blood transplants,

  • there are thousands of HLA types,

  • and even siblings and close relatives may not have compatible bone marrow.

  • If this is the case, the search is expanded to a database

  • containing the genetic makeup of millions of voluntary bone marrow donors.

  • The more potential donors there are,

  • the more patients lives can be saved through successful transplants.

  • Leukemia may be a frightening disease, but there is strength and hope in numbers.

Despite advances in medicine,

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B2 TED-Ed bone marrow marrow bone leukemia blood

【TED-Ed】What is leukemia? - Danilo Allegra and Dania Puggioni

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    稲葉白兎 posted on 2016/01/04
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