Despite advances in medicine, cancer remains one of the most frightening diagnoses patients can receive.
尽管医学在进步，癌症仍是患者们最怕听到的诊断结果。
What makes it so difficult to cure is that it's not one illness,
使它难以治愈的原因是，它并不是一个单一的病变，
but a family of over 100 diseases occurring in different types of cells.
而是在不同的细胞内发生的超过100种病变的统称。
And one type of cancer has the unfortunate distinction of afflicting children more than any other type.
其中有一种癌症给儿童带来的折磨比其它任何一种癌症都更加难熬。
This is leukemia, a cancer that begins in stem cells found in the bone marrow.
这就是白血病，一种始于骨隧中干细胞的癌症。
A stem cell is a bit like an infant, undeveloped but possessing great potential.
干细胞有点儿像一个婴儿，还未充分发育但潜能巨大。
Many stem cells specialize and become cells of organs, like the liver, brain and heart.
许多干细胞经过分化变成器官细胞，例如肝脏、大脑和心脏。
But in some tissues, they can continue to divide into new stem cells throughout development,
但在某些组织中，它们将继续分裂产生新的干细胞，
and into adulthood in order to frequently generate new cells and keep up with the body's needs.
而后再分化成熟以跟上身体生长发育需求。
One example is the bone marrow, where stem cells differentiate into many types of blood cells.
其中一个例子就是骨髓，其中的干细胞将分化为多种血细胞。
That includes red blood cells, which carry oxygen from the lungs to all tissues,
包括红血球，用于将氧气从肺输送到所有组织，
platelets, which help stop bleeding by sticking to damaged blood vessels,
血小板，堵住受伤的血管以止血，
and white blood cells, which patrol the body, destroying potentially harmful invaders.
以及白血球，它们负责守护身体，摧毁潜在的有害入侵者。
Every once in a while, something goes wrong during a stem cell's specialization process
有时干细胞在分化过程中会出问题，
and harmful mutations occur in the cell's DNA.
细胞DNA会出现有害突变。
Cells with compromised DNA are supposed to self-destruct,
受损DAN的细胞一般会凋亡，
but some damaged cells ignore this order, replicating uncontrollably, even as they lose their original function.
但有些受损细胞没有遵守这个规律，而是不受控制的不断复制，尽管它们已失去了原有的功能。
These are what we know as cancer cells.
这就是我们所说的癌细胞。
It is not yet clear why leukemia is the most common childhood cancer,
为什么白血病是儿童最易患的癌症还尚未知晓，
but one contributing factor may be that leukemias are often caused by just one or two DNA modifications,
但原因之一可能是一两个DNA位点突变就能使白血病细胞产生，
while most cancers require many of them, allowing leukemias to arise faster than other types of cancer.
而其他癌症则需要多个DNA位点的突变，这就使得白血病比其他癌症发病快得多。
Moreover, some DNA alterations can occur in white blood cells during fetal development,
此外，白细胞中某些DNA改变在胎儿时期就能发生，
further increasing the risk of early leukemia.
所以增加了早期患白血病的风险。
But though it affects more children than any other cancer, adults constitute the majority of leukemia patients overall.
尽管比其他癌症，儿童更容易得白血病，但总的来说成人白血病患者还是占大多数的。

Once leukemia strikes, the damaged cells reproduce in the blood and the bone marrow
患病后，受损细胞会在血液和骨髓里不断复制，
until they take up all available space and resources.
直到它们侵占所有空间和资源。
When the bone marrow can no longer produce the required amount of functional cells, the blood becomes depleted.
当骨髓不能产生足够数量的功能正常的细胞时，血液便枯竭了。
The lack of red blood cells means that muscles don't get enough oxygen,
红血球的缺乏意味着肌肉得不到足够的氧气，
the reduced number of platelets is not sufficient to repair wounds,
血小板数量的减少也使得伤口难以修复，
and the dearth of functional white blood cells impairs the immune system, increasing the risk of infections.
而功能性白细胞的缺乏降低了免疫力，增加了受感染的风险。
To restore the normal function of the blood, leukemic cells have to be eliminated.
要重建正常的血液系统，白血病细胞需要被清除。
But because leukemias are not solid tumors, they can't be removed surgically.
但因为白血病并非实体瘤，所以它无法通过手术切除。
Instead, the cells are killed inside the body using various treatments that include chemotherapy,
不过存在许多其他方法能消灭体内的白血病细胞，包括化疗，
a combination of drugs that destroys quickly multiplying cells.
也就是一系列药物，可杀死快速复制的细胞。
Unfortunately, this has the side effect of killing healthy cells, such as those found in hair follicles or intestines.
遗憾的是，这种疗法也会杀死健康的细胞，例如毛囊或肠道。
And in some cases, the dosage required is so high that it kills all cells in the bone marrow, including stem cells.
有一些情况下，化疗需要的药量很大，会杀死骨髓里全部的细胞，包括干细胞。
When this happens, the body is no longer able to create new blood cells on its own.
这种情况下，身体无法自己产生新的血细胞。
Fortunately, outside help can come in the form of stem cells from the bone marrow of a donor.
幸运的是，干细胞可以从他人中获得，也就是骨髓捐献者。
Once transplanted into the patient, they rapidly repopulate the bone marrow and the blood.
当骨髓被移植到患者身体后，它会迅速产生骨髓和血液。
However, bone marrow transplants are a complicated process requiring antigen compatibility between the donor and recipient
然而，骨髓移植的过程很复杂，它要求捐献者和患者间的抗原能够匹配，
to keep the transplanted cells from from attacking the patient's own cells as foreign bodies.
这样才能防治移植的细胞攻击患者自身。
Unlike with blood transplants, there are thousands of HLA types,
细胞与输血不同，HLA（人类白细胞抗原）有几千种，
and even siblings and close relatives may not have compatible bone marrow.
甚至患者与兄弟姐妹、近亲的HLA都不一定能相容。
If this is the case, the search is expanded to a database
这时，就得在数据库进行搜寻，
containing the genetic makeup of millions of voluntary bone marrow donors.
数据库录入了数百万骨髓捐献者的基因。
The more potential donors there are, the more patients lives can be saved through successful transplants.
骨髓捐献者越多，能通过骨髓移植被救治的患者就越多。
Leukemia may be a frightening disease, but there is strength and hope in numbers.
白血病固然可怕，但人多，力量和希望就大。