Colorectal Cancer
What is cancer?
The body is made up of trillions of living cells. Normal body cells grow, divide into new
cells, and die in an orderly way. During the early years of a person's life, while they are still
growing, their normal cells divide faster. Once the person becomes an adult, most cells
divide only to replace worn-out or dying cells or to repair injuries.
Cancer begins when cells in a part of the body start to grow out of control. There are many
kinds of cancer, but they all start because of out-of-control growth of abnormal cells.
Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells
continue to grow and form new, abnormal cells. In most cases the cancer cells form a tumor.
Cancer cells can also invade (grow into) other tissues, something that normal cells cannot do.
Growing out of control and invading other tissues are what makes a cell a cancer cell.
Cells become cancer cells because of damage to DNA. DNA is in every cell and directs all its
actions. In a normal cell, when DNA is damaged the cell either repairs the damage or the cell
dies. In cancer cells, the damaged DNA is not repaired, but the cell doesn't die like it should.
Instead, this cell goes on making new cells that the body does not need. These new cells will
all have the same damaged DNA as the first abnormal cell does.
People can inherit damaged DNA, but most often the DNA damage is caused by mistakes
that happen while the normal cell is reproducing or by something in our environment.
Sometimes the cause of the DNA damage is something obvious, like cigarette smoking. But
often no clear cause is found.
Cancer cells often travel to other parts of the body, where they begin to grow and form new
tumors that replace normal tissue. This process is called metastasis. It happens when the
cancer cells get into the bloodstream or lymph vessels of our body.
No matter where a cancer may spread, it is always named for the place where it started. For
example, breast cancer that has spread to the liver is still called breast cancer, not liver cancer
Different types of cancer can behave very differently. For example, lung cancer and breast
cancer are very different diseases. They grow at different rates and respond to different
treatments. This is why people with cancer need treatment that is aimed at their particular
kind of cancer.
Not all tumors are cancerous. Tumors that aren't cancer are called benign. Benign tumors can
cause problems – they can grow very large and press on healthy organs and tissues. But they
cannot grow into (invade) other tissues. Because they can’t invade, they also can't spread to
other parts of the body (metastasize). These tumors are rarely life threatening.
What is colorectal cancer?
Colorectal cancer is a term used for cancer that starts in the colon or the rectum. These
cancers can also be referred to separately as colon cancer or rectal cancer, depending on
where they start. Colon cancer and rectal cancer have many features in common. They are
discussed together in this document except for the section about treatment, where they are
discussed separately.
The normal digestive system
The colon and rectum are parts of the digestive system, which is also called the
gastrointestinal (GI) system (see illustration). The first part of the digestive system (the
stomach and small intestine) processes food for energy while the last part (the colon and
rectum) absorbs fluid to form solid waste (fecal matter or stool) that then passes from the
body. To understand colorectal cancer, it helps to know something about the normal structure
of the digestive system and how it works.
After food is chewed and swallowed, it travels through the esophagus to the stomach. There
it is partly broken down and then sent to the small intestine, also known as the small bowel. It
is called small because it is narrower than the large intestine (colon and rectum), but actually
the small intestine is the longest segment of the digestive system ─ about 20 feet. The small
intestine continues breaking down the food and absorbs most of the nutrients.
The small intestine joins the large intestine (or large bowel) in the right lower abdomen. Most
of the large intestine is made up of the colon, a muscular tube about 5 feet long. The colon
absorbs water and salt from the food matter and serves as a storage place for waste matter.
The colon has 4 sections:
· The first section is called the ascending colon. It starts with a small pouch (the cecum)
where the small bowel attaches to the colon and extends upward on the right side of the
abdomen. The cecum is also where the appendix attaches to the colon.
· The second section is called the transverse colon since it goes across the body from the
right to the left side in the upper abdomen.
· The third section, called the descending colon, continues downward on the left side.
· The fourth and last section is known as the sigmoid colon because of its "S" or "sigmoid"
shape.
The waste matter that is left after going through the colon is called feces or stool. It goes into