NCCN Guidelines for Patients
Breast Cancer - Carcinoma in Situ
, Version 1.2016
Cancer is a disease of cells. Inside of cells are coded
instructions for building new cells and controlling
how cells behave. These instructions are called
genes. Genes are a part of DNA (
cid), which is grouped together into bundles called
See Figure 1.2
. Abnormal changes
(mutations) in genes cause normal cells to become
cancer cells. Researchers are still trying to learn what
causes genes to mutate and cause cancer.
Cancer cells don’t behave like normal cells in three
key ways. First, mutations in genes cause normal
cells to grow more quickly and live longer. Normal
cells grow and then divide to form new cells when
needed. They also die when old or damaged as
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
The second way cancer cells differ from normal
cells is that they can grow into surrounding tissues.
If not treated, the primary tumor can extend beyond
the walls of lobules or ducts into the stroma. Breast
cancers that haven’t grown into the stroma are called
“noninvasive” and breast cancers that have grown
into the stroma are called “invasive.” DCIS is a
noninvasive breast cancer.
Third, unlike normal cells, invasive cancer cells can
leave the breast and form tumors in other parts of
the body. This process is called metastasis. In this
process, cancer cells break away from the tumor and
Carcinoma in situ
Figure 1.2 Genetic material in cells
Most human cells contain the “blueprint of life”—the plan by which our bodies are made
and work. The plan is found inside of chromosomes, which are long strands of DNA that are
tightly wrapped around proteins. Genes are small pieces of DNA that contain instructions
for building new cells and controlling how cells behave. Humans have about 24,000 genes.
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