NCCN Guidelines for Patients
Rectal Cancer, Version 1.2017
A disease of cells
Your body is made of trillions of cells. Cancer is a
disease of cells. Each type of cancer is named after
the cell from which it derived. Rectal cancer is a
cancer of rectal cells.
Almost all rectal cancers are adenocarcinomas.
Adenocarcinomas are cancers of cells that line
glands and, in the case of rectal cancer, make
mucus. Adenocarcinomas of the rectum are the focus
of this book.
Cells have a control center called the nucleus.
The nucleus contains chromosomes, which are
long strands of DNA (
wrapped around proteins.
See Figure 3
DNA are coded instructions for building new cells and
controlling how cells behave. These instructions are
There can be abnormal changes in genes called
mutations. Some types of mutations that are linked
to cancer are present in all cells. Other mutations are
present only in cancer cells. Mutations cause cancer
cells to not behave like normal cells and, sometimes,
to look very different from normal cells.
Cancer cells don’t behave like normal cells in three
key ways. First, cancer cells grow more quickly and
live longer than normal cells. Normal cells grow
and then divide to form new cells when needed.
They also die when old or damaged as shown in
. In contrast, cancer cells make new cells
that aren’t needed and don’t die quickly when old or
damaged. Over time, cancer cells form a mass called
the primary tumor.
The second way cancer cells differ from normal cells
is that they can grow into surrounding tissues. If not
treated, the primary tumor can grow through the
rectal wall. Cancer cells can even grow into nearby
structures. Rectal cancers that haven’t grown into the
second layer of the rectal wall are called “noninvasive
cancers.” Rectal cancers that have grown into the
second layer are called “invasive cancers.”
Third, unlike normal cells, cancer cells can leave
the rectum. This process is called metastasis. In this
process, cancer cells break away from the tumor and
merge with blood or lymph. Then, the cancer cells
travel in blood or lymph through vessels to other
sites. Once in other sites, cancer cells may form
secondary tumors and cause major health problems.
Rectal cancer basics
A disease of cells