1
00:00:06,938 --> 00:00:09,008
Despite advances in medicine,

2
00:00:09,008 --> 00:00:14,018
cancer remains one of the most frightening
diagnoses patients can receive.

3
00:00:14,018 --> 00:00:18,188
What makes it so difficult to cure
is that it's not one illness,

4
00:00:18,188 --> 00:00:23,559
but a family of over 100 diseases
occurring in different types of cells.

5
00:00:23,559 --> 00:00:26,452
And one type of cancer 
has the unfortunate distinction

6
00:00:26,452 --> 00:00:29,810
of afflicting children 
more than any other type.

7
00:00:29,810 --> 00:00:31,730
This is leukemia,

8
00:00:31,730 --> 00:00:35,705
a cancer that begins in stem cells
found in the bone marrow.

9
00:00:35,705 --> 00:00:38,342
A stem cell is a bit like an infant,

10
00:00:38,342 --> 00:00:41,651
undeveloped but possessing 
great potential.

11
00:00:41,651 --> 00:00:44,830
Many stem cells specialize
and become cells of organs,

12
00:00:44,830 --> 00:00:47,719
like the liver, brain and heart.

13
00:00:47,719 --> 00:00:49,033
But in some tissues,

14
00:00:49,033 --> 00:00:52,993
they can continue to divide into new 
stem cells throughout development,

15
00:00:52,993 --> 00:00:57,189
and into adulthood in order to frequently
generate new cells

16
00:00:57,189 --> 00:00:59,342
and keep up with the body's needs.

17
00:00:59,342 --> 00:01:01,694
One example is the bone marrow,

18
00:01:01,694 --> 00:01:05,576
where stem cells differentiate
into many types of blood cells.

19
00:01:05,576 --> 00:01:07,698
That includes red blood cells,

20
00:01:07,698 --> 00:01:10,491
which carry oxygen 
from the lungs to all tissues,

21
00:01:10,491 --> 00:01:14,532
platelets, which help stop bleeding
by sticking to damaged blood vessels,

22
00:01:14,532 --> 00:01:16,139
and white blood cells,

23
00:01:16,139 --> 00:01:20,250
which patrol the body,
destroying potentially harmful invaders.

24
00:01:20,250 --> 00:01:21,636
Every once in a while,

25
00:01:21,636 --> 00:01:25,196
something goes wrong during 
a stem cell's specialization process

26
00:01:25,196 --> 00:01:28,528
and harmful mutations 
occur in the cell's DNA.

27
00:01:28,528 --> 00:01:32,421
Cells with compromised DNA
are supposed to self-destruct,

28
00:01:32,421 --> 00:01:34,962
but some damaged cells ignore this order,

29
00:01:34,962 --> 00:01:39,778
replicating uncontrollably,
even as they lose their original function.

30
00:01:39,778 --> 00:01:42,344
These are what we know as cancer cells.

31
00:01:42,344 --> 00:01:46,847
It is not yet clear why leukemia
is the most common childhood cancer,

32
00:01:46,847 --> 00:01:48,668
but one contributing factor may be

33
00:01:48,668 --> 00:01:53,486
that leukemias are often caused
by just one or two DNA modifications,

34
00:01:53,486 --> 00:01:56,377
while most cancers require many of them,

35
00:01:56,377 --> 00:02:00,611
allowing leukemias to arise faster
than other types of cancer.

36
00:02:00,611 --> 00:02:04,815
Moreover, some DNA alterations
can occur in white blood cells

37
00:02:04,815 --> 00:02:06,625
during fetal development,

38
00:02:06,625 --> 00:02:09,331
further increasing the risk 
of early leukemia.

39
00:02:09,331 --> 00:02:12,110
But though it affects more children
than any other cancer,

40
00:02:12,110 --> 00:02:16,037
adults constitute the majority
of leukemia patients overall.

41
00:02:16,037 --> 00:02:21,001
Once leukemia strikes, the damaged cells
reproduce in the blood and the bone marrow

42
00:02:21,001 --> 00:02:24,531
until they take up 
all available space and resources.

43
00:02:24,531 --> 00:02:26,622
When the bone marrow 
can no longer produce

44
00:02:26,622 --> 00:02:28,898
the required amount of functional cells,

45
00:02:28,898 --> 00:02:30,671
the blood becomes depleted.

46
00:02:30,671 --> 00:02:32,112
The lack of red blood cells

47
00:02:32,112 --> 00:02:34,841
means that muscles 
don't get enough oxygen,

48
00:02:34,841 --> 00:02:38,661
the reduced number of platelets
is not sufficient to repair wounds,

49
00:02:38,661 --> 00:02:42,930
and the dearth of functional white
blood cells impairs the immune system,

50
00:02:42,930 --> 00:02:45,332
increasing the risk of infections.

51
00:02:45,332 --> 00:02:47,484
To restore the normal 
function of the blood,

52
00:02:47,484 --> 00:02:49,739
leukemic cells have to be eliminated.

53
00:02:49,739 --> 00:02:52,111
But because leukemias 
are not solid tumors,

54
00:02:52,111 --> 00:02:54,458
they can't be removed surgically.

55
00:02:54,458 --> 00:02:58,506
Instead, the cells are killed
inside the body using various treatments

56
00:02:58,506 --> 00:03:00,490
that include chemotherapy,

57
00:03:00,490 --> 00:03:04,666
a combination of drugs that destroys
quickly multiplying cells.

58
00:03:04,666 --> 00:03:07,972
Unfortunately, this has the side effect
of killing healthy cells,

59
00:03:07,972 --> 00:03:11,412
such as those found in hair follicles
or intestines.

60
00:03:11,412 --> 00:03:14,463
And in some cases, the dosage 
required is so high

61
00:03:14,463 --> 00:03:16,683
that it kills all cells 
in the bone marrow,

62
00:03:16,683 --> 00:03:19,047
including stem cells.

63
00:03:19,047 --> 00:03:24,285
When this happens, the body is no longer
able to create new blood cells on its own.

64
00:03:24,285 --> 00:03:28,269
Fortunately, outside help can come
in the form of stem cells

65
00:03:28,269 --> 00:03:30,354
from the bone marrow of a donor.

66
00:03:30,354 --> 00:03:32,993
Once transplanted into the patient,

67
00:03:32,993 --> 00:03:35,915
they rapidly repopulate 
the bone marrow and the blood.

68
00:03:35,915 --> 00:03:38,997
However, bone marrow transplants
are a complicated process

69
00:03:38,997 --> 00:03:43,041
requiring antigen compatibility
between the donor and recipient

70
00:03:43,041 --> 00:03:46,512
to keep the transplanted cells from
from attacking the patient's own cells

71
00:03:46,512 --> 00:03:48,352
as foreign bodies.

72
00:03:48,352 --> 00:03:49,836
Unlike with blood transplants,

73
00:03:49,836 --> 00:03:51,964
there are thousands of HLA types,

74
00:03:51,964 --> 00:03:56,529
and even siblings and close relatives
may not have compatible bone marrow.

75
00:03:56,529 --> 00:04:00,245
If this is the case, the search 
is expanded to a database

76
00:04:00,245 --> 00:04:05,057
containing the genetic makeup of millions
of voluntary bone marrow donors.

77
00:04:05,057 --> 00:04:07,153
The more potential donors there are,

78
00:04:07,153 --> 00:04:11,652
the more patients lives can be saved
through successful transplants.

79
00:04:11,652 --> 00:04:16,912
Leukemia may be a frightening disease,
but there is strength and hope in numbers.