Newly Diagnosed / Understanding Your Cancer The
breast is a milk factory in which the lobules make the milk and the
ducts carry the milk to the nipples. Virtually all breast cancer begins
in this milk ductal system.
Cancer occurs when a normal cell stops functioning properly and begins
to grow and divide uncontrollably. This process doesn't occur in a day,
or in a week, or in a month, or even in a year. It often takes decades
or more for a normal cell to acquire the properties necessary to start
acting like a cancer cell.
The first step to understanding cancer is becoming familiar with the following terms:
Cell:
The cell is the structural and functional unit of all living organisms.
It is estimated that the human body contains 100,000 billion cells.
Nucleus:
The nucleus is the central part of the cell. It contains DNA and RNA
and is responsible for the cell's growth and reproduction.
DNA (deoxyribonucleic acid):
The DNA in the nucleus codes all the information in our body and is
responsible for transferring genetic characteristics. With the same
system of four bases (like four letters), everything that's alive is
programmed. These four bases, or nucleotides, are adenosine
(represented by the letter A), thymine (T), cytosine (C), and guanine
(G). The nucleotides combine in pairs, and this pairing is very
precise, like a tiny jigsaw puzzle. A and T fit together, as do G and
C, and that can never vary.
Gene:
The base pairs of DNA come together in a chain to form a gene. Genes
are the basic biological units of heredity. Genes are arranged in a
long row, side by side, to form a chromosome.
Chromosome:
Normal human cells have 46 chromosomes that are arranged in 23 pairs.
All the chromosomes together form the genome — a human being.
Protein: A large molecule that performs a variety of essential functions in the cell. Proteins are the body's building blocks.
RNA (ribonucleic acid):
DNA doesn't work alone. It has a partner, called RNA. RNA duplicates
each gene and translates the genetic code it contains in its DNA into a
protein. The production of RNA determines how much protein will be
produced and therefore the levels of expression of a particular
protein.
Putting this together:
The DNA that forms each gene in a chromosome is a code for creating a
protein. But the DNA can't make that protein alone. It needs RNA to
translate the code and produce the protein. You can think of it this
way: DNA holds the precious family recipe for making, in this case,
protein. RNA is the copy that you use in the kitchen to make the
protein. [Enlarge image]
Now that you know about DNA, RNA, and proteins, it's time to learn about the cell cycle. The Cell Cycle
Cell division, which is termed mitosis, is carefully orchestrated in a
process called the cell cycle. The active cell cycle is divided into
four different phases. The quiescent phase, G0, is the phase most cells
are usually in. They're just sitting around, doing nothing. Then
something wakes them up and says, "Time to divide!" sending them into
the first active phase, called G1. During this phase, which lasts
approximately nine hours, the cells prepare to divide.
Before a cell can move on to the next phase, it is inspected to ensure
that it is free of any serious mutations. If mutations are present, the
cell must repair them before the G1 checkpoint will allow it to move on
to the second active phase, which is called the S phase. During the S
phase, which lasts about six hours, the cell replicates its entire
genetic material, which results in two sets of paired chromosomes. The
cell then enters the third active phase, which is called G2. This
phase, which takes about four hours, involves another quality control
inspection, and, if necessary, repair. It is the final checkpoint
before the cell enters the mitosis, or M, phase, where it will divide
and become two cells.
All
cells, including cancer cells, go through the same cell cycle. Now that
you are familiar with what goes on inside the cell and the cell cycle,
the next step is to look at how cancer develops.
How Cancer Develops
A cancerous cell is a normal cell that has stopped functioning properly
and is now growing and dividing uncontrollably. This occurs when normal
processes break down. What happens?
Mutations Develop:
A mutation is an error that can occur when the wrong nucleotide—A, T,
C, or G—gets inserted into a gene as it's being created. A mutation can
also occur if a nucleotide is deleted. A person can be born with a
mutation. Mutations also develop throughout a person's lifetime. Most
mutations will never cause a problem. It is estimated that thousands of
DNA errors are detected and repaired during the cell division process.
One mutation by itself isn't enough for a normal cell to stop
functioning properly. It takes a series of mutations for a cell to
transform from normal to cancerous. This is why most cancers, including
breast cancer, are more likely to occur as people age.
Where the mutation occurs is also important. For example, P53 is a
tumor suppressor gene that works at the G1 checkpoint. Like any other
gene, P53 can become mutated. If this occurs, the G1 checkpoint will no
longer function properly. This allows cells that contain mutations and
should have been sent back for repairs through, increasing the
possibility that a cell will collect enough mutations to become cancer.
A mutation can also develop in
an oncogene, a gene that is involved with cell division. Oncogenes
involved in breast cancer typically encourage cells to divide faster.
One oncogene that comes into play in breast cancer is epidermal growth
factor receptor 2. In the US this is commonly known as HER2 (or HER-2
or Her-2/neu); in Europe it is called erB2 or erb-b2. When a mutation
occurs in HER2, the gene becomes amplified. This means that the cell
carries 10 to 60 copies of the gene instead of just one. Too many genes
result in too many HER2 receptors on the cell's surface and an excess
of HER2 protein. This extra protein causes the cell to replicate more
than it should. Breast cancer tumors that have this gene amplification
are called HER2-positive.
Cells with Mutations That Should Die Don't:
All cells have the ability to kill themselves. This programmed cell
death, or cell suicide, is called apoptosis, and it is designed to
occur when there is something wrong with the cell itself—such as too
many mistakes, or mutations, in the DNA. Cancer cells acquire the
ability to evade apoptosis, which allows them to keep replicating
endlessly.
Cells Keep Dividing Endlessly:
Cells are not supposed to keep dividing forever. They are only supposed
to divide for a set number of times. At the very end of each chromosome
is a section called the telomere. Each time a cell divides, it snips
off a little bit of the telomere. When the telomere gets really short,
it sends a message to the cell to stop dividing. Telomerase is an
enzyme in the body that can lengthen the telomere. Cancer cells use
telomerase to keep the telomere from getting too short. This allows the
cancer cell to replicate endlessly.
Inside the Breast: From Precancer to Invasive Breast Cancer
A person can have millions of cells with mutations in his or her body
and not have cancer. For someone to have cancer, the cells must be
replicating endlessly. Further, this mass of cells has to break out of
the area where these cells are supposed to be and invade into other
areas.
Virtually all breast
cancer begins in the breast duct. A diagnosis of ductal carcinoma in
situ (DCIS) or lobular carcinoma in situ (LCIS) means that there are
cancer cells in the breast, but they are still contained within the
breast duct or lobule. They have not invaded into another area. This is
why DCIS and LCIS are called precancers. If a woman is diagnosed with
invasive cancer, it means the cancerous cells have broken out of the
duct and invaded the surrounding tissue.
Most invasive breast cancers have been present for 8 to 10 years by the
time they have been detected on a mammogram or physical exam. During
that time there is plenty of opportunity for the cancer cells to get
out of the breast and spread to the rest of the body. Sometimes the
immune system takes care of these cells and sometimes it doesn't.
If cancer cells were content with only invading nearby tissue, cancer
would be easy to cure. But they aren't. Their next goal is to make new
blood vessels to support themselves (a process called angiogenesis),
get out of the breast territory, and establish new homes for themselves
in other parts of the body. This is called metastasis.
Metastatic Disease
In order to metastasize, cancer cells have to evade the body's immune
system, make new blood vessels, travel through the bloodstream, figure
out what organ to go to, break out of the blood vessel, get into the
new organ, and set up a new home. But even when early metastasis has
occurred, it doesn't necessarily spell doom. Let's say that the cell
has successfully made the journey to the lung. Once it arrives there it
has to establish a new home by making new blood vessels. It's possible
that other cells in the lung may be able to keep these invaders under
control. The cells then act normally until something happens—a change
in the lung's environment, or a new genetic alteration occurs that
allows the breast cancer cells to grow in the lung. This might explain
why some women will have a recurrence of breast cancer many years after
the first diagnosis. Those cells were there from the beginning but were
dormant until the right conditions induced them to grow again.
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