Breast Cancer: What Happens in the Body?

Medically Reviewed by Hansa D. Bhargava, MD on January 24, 2021

One of the most difficult parts of having breast cancer is the unknown. How did you get this disease? Will treatments help? How long might you live?

Here’s what to know about breast cancer, the most common form of cancer in American women except for skin cancer.

How Does Breast Cancer Start?

All cancers start the same way, when cells grow faster than they should. Normally, your cells divide and make new cells to replace old cells that die off.

But cancer cells have changes in their DNA that let off uncontrolled cell growth. You may have inherited these faulty genes from your parents. Or you could have been exposed to things in the environment that damaged the DNA.

In breast cancer, the abnormal cells grow in the small tubes (ducts) that carry milk to the nipples or in the glands (lobules) that make milk inside your breasts. These growths are called tumors.

How Does Breast Cancer Spread?

Cancer cells start in your breast, but they can travel. A few cells can get loose from the tumor and spread to other parts of the same breast. From there, the cancer cells can get into your bloodstream or lymph nodes and reach other parts of your body.

The most common places for breast cancer to spread are the:

Breast cancer that spreads to these organs is called metastatic or late-stage breast cancer.

Some people are already at a late stage when their cancer is diagnosed. Other breast cancers are caught early, but then spread.

How Do Hormones Fuel Breast Cancer?

Some breast cancers have proteins called receptors on their surface. Receptors are like locks. The hormones estrogen and/or progesterone fit into the receptors like keys. When these hormones lock onto their receptor, they send out signals that help the cancer grow.

Estrogen helps some breast cancers grow. Progesterone helps other cancers grow. Some cancers respond to both hormones. These are called hormone receptor-positive breast cancers. Your doctor will test your breast cancer cells for estrogen and/or progesterone receptors to find the right treatment for you.

How Do Breast Cancer Treatments Help?

Doctors can pick from several treatment options. Your therapy will depend on your type of breast cancer and how far it has spread. You may get more than one treatment.

Surgery removes as much of the cancer as possible. If the cancer is small, your doctor might take out just the part of the breast where the cancer is (lumpectomy or partial mastectomy). For a larger cancer, the surgeon might remove the whole breast (mastectomy) or both breasts (double mastectomy). The surgeon can also take out nearby lymph nodes.

Chemotherapy uses strong medicine that travels through your bloodstream to kill cancer cells or to stop them from dividing. You can have this treatment after surgery to get rid of any remaining cancer cells, or if your cancer has spread.

Radiation zaps cancer cells with high-energy rays. You get it after surgery to kill any leftover cancer, or to treat cancer that has spread to areas like your bones or brain.

Hormone therapy treats breast cancers that respond to estrogen and/or progesterone. It lowers the amount of estrogen in your body or blocks the effects of estrogen so that it can't help your cancer grow.

Targeted therapy works against breast cancers that use proteins such as HER2 to help them grow.

Immunotherapyboosts your immune system to help it find and destroy breast cancer cells. Some of these treatments take the brakes off your immune cells so they can attack the cancer.

What are the Chances of Survival?

It's normal to wonder how long you might live. Doctors use the term "relative survival rate" to predict what percentage of people with certain stages of breast cancer will live for 5 years, compared to peers who don't have breast cancer.

The 5-year relative survival rates for breast cancer are:

  • 99% for early-stage cancers (meaning 99 out of 100 people with breast cancer will reach their expected lifespan)
  • 86% for cancer that has spread in the area of the original tumor
  • 27% for cancers that have spread to other parts of the body

These numbers are based on research done on large groups of people with breast cancer. Your survival rate could be different based on things like your age, health, and how well your cancer responds to treatment.

Can Breast Cancer Come Back?

When you go into remission, it means there are no more signs of cancer in your body. But it’s possible for the cancer to come back in the future. This is called a recurrence. Breast cancer can come back in the same place you had it before, or appear in another part of your body.

You're most likely to have a recurrence in the first 2 years after your treatment. Your risk then slowly drops. Your doctor will check you at regular intervals to check for signs of a new breast cancer.

Ask your doctor and other members of your treatment team to explain anything you don't understand. And if you feel overwhelmed, get help from a counselor or therapist.

WebMD Medical Reference



American Cancer Society: "Breast Cancer Hormone Receptor Status," "Choosing a Cancer Counselor," "Follow up Care After Breast Cancer Treatment," "How Does Breast Cancer Form?" "Immunotherapy for Breast Cancer," "Radiation for Breast Cancer," "Survival Rates for Breast Cancer," "Targeted Drug Therapy for Breast Cancer."

Breast Cancer Now: "Prognosis." "Chemotherapy," "How Chemotherapy Works," "Metastatic Breast Cancer," "Recurrent Breast Cancer," "What Is Hormonal Therapy?"

CDC: "How is Breast Cancer Treated?"

Johns Hopkins Medicine: "Breast Cancer Recurrence."

Mayo Clinic: "Breast Cancer."

Moffitt Cancer Center: "Where Does Breast Cancer Metastasize To?"

National Cancer Institute: "What Is Cancer?"

OSF Healthcare: "Questions to ask after a cancer diagnosis."

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