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NCCN Guidelines for Patients


Breast Cancer - Carcinoma in Situ

(stage 0)

, Version 1.2016

Understanding cancer

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

shown in

Figure 1.3


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 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

Understanding cancer

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.

Illustration Copyright © 2016 Nucleus Medical Media, All rights reserved.