Skip to Content Skip to Footer

What is Breast Cancer?

Breast cancer is a malignant tumor that develops from cells in the breast that change and grow out of control. Breast cancer commonly begins either in the cells of the lobules, which are the milk-producing glands, or the ducts, the passages that drain milk from the lobules to the nipple. Less commonly, breast cancer begins in the stromal tissues, which include the fatty and fibrous connective tissues of the breast. Breast cancer can spread outside the breast through blood vessels and lymph vessels. When breast cancer spreads to other parts of the body, it is said to have metastasized.

Breast cancer is the second most common cancer in women after skin cancer in the United States. According to the American Cancer Society, about 1 in 8 U.S. women will develop invasive breast cancer throughout their lifetime. Breast cancer can occur in both men and women, but it is very rare in men.


The type of breast cancer is determined by the specific cells in the breast that are affected. The type of breast cancer can also refer to whether the cancer has spread to other areas of the body. In situ breast cancer (ductal carcinoma in situ or DCIS) is a cancer that starts in a milk duct and has not grown into the rest of the breast tissue. The term invasive breast cancer is used to describe any type of breast cancer that has spread into the surrounding breast tissue.

The most common types of breast cancer are:

  • Invasive ductal carcinoma – The cancer cells begin in the ducts and then grow outside the ducts into other parts of the breast tissue. Invasive cancer cells can also spread, or metastasize, to other parts of the body.
  • Invasive lobular carcinoma – Cancer cells begin in the lobules and then spread from the lobules to the breast tissues that are close by. These invasive cancer cells can also spread to other parts of the body.


Different people have different symptoms of breast cancer and some people do not have any signs or symptoms at all. The most common symptom of breast cancer is a new lump or mass.

Some warning signs of breast cancer may include:

  • New lump in the breast or underarm
  • Thickening or swelling of part of the breast
  • Irritation or dimpling of breast skin
  • Redness or flaky skin in the nipple area or the breast
  • Pulling in of the nipple or pain in the nipple area
  • Nipple discharge other than breast milk, including blood
  • Any change in the size or the shape of the breast
  • Pain in any area of the breast

Please remember that these symptoms can happen with other conditions that are not cancer. If you have any signs or symptoms that worry you, be sure to speak to your physician.



Finding breast cancer early and getting state-of-the-art cancer treatment are the most important strategies to prevent deaths from breast cancer. Breast cancer that is found early, when it is small and has not spread, is easier to treat successfully. Getting regular screening tests, such as mammograms, is the most reliable way to find breast cancer early. 

Physicians often use additional tests to find or diagnose breast cancer.

  • Breast ultrasound – A machine that uses sound waves to make pictures, called sonograms, of areas inside the breast.
  • Diagnostic mammogram – If you have a problem in your breast, such as lumps, or if an area of the breast looks abnormal on a screening mammogram, doctors may have you get a diagnostic mammogram. This is a more detailed X-ray of the breast.
  • Breast magnetic resonance imaging (MRI) – A kind of body scan that uses a magnet linked to a computer. The MRI scan will make detailed pictures of areas inside the breast.
  • Biopsy – This is a test that removes tissue or fluid from the breast to be looked at under a microscope and do more testing. There are different kinds of biopsies (for example, fine-needle aspiration, core biopsy, or open biopsy).

If the diagnosis is breast cancer, the next step is to determine the stage of the cancer through tests. The stage of a cancer describes how much cancer is in the body, helps determine how serious the cancer is, and how best to treat it. Your physician identifies the stage of cancer by determining:

  • Whether the cancer is invasive or noninvasive
  • The size of the tumor
  • The number of lymph nodes affected
  • The cancer’s presence in other parts of the body

The five stages of breast cancer are:

Stage 0

In stage 0, the cancer is considered noninvasive. There are two types of stage 0 breast cancer:

  • In ductal carcinoma in situ (DCIS), the cancer is found inside the lining of the milk ducts but hasn’t spread to other breast tissue.
  • While lobular carcinoma in situ (LCIS) is also classified as a stage 0 breast cancer, it is not considered cancer. Instead, it describes abnormal cells that have formed in the lobules of the breast.

Stage 0 breast cancer is highly treatable.

Stage 1

At this stage, the cancer is considered invasive but localized. Stage 1 is divided into 1A and 1B forms:

  • In stage 1A, the cancer is smaller than 2 centimeters (cm). It has not spread to the surrounding lymph nodes.
  • In stage 1B, your doctor might not find a tumor in your breast, but the lymph nodes may have tiny groupings of cancer cells. These groupings measure between 0.2 and 2 millimeters (mm).

As with stage 0, stage 1 breast cancer is highly treatable.

Stage 2

The cancer is invasive in stage 2. This stage is divided into 2A and 2B:

  • In stage 2A, you may have no tumor, but the cancer has spread to your lymph nodes. Alternatively, the tumor might be less than 2 cm in size and involves the lymph nodes, or the tumor may measure between 2 and 5 cm but doesn’t involve your lymph nodes.
  • In stage 2B, the tumor size is larger. You may be diagnosed with 2B if the tumor is between 2 to 5 cm and it has spread to four or fewer lymph nodes. Otherwise, the tumor might be bigger than 5 cm with no lymph node spread.

Stage 2 is treatable, sometimes requiring stronger treatment than earlier stages.

Stage 3

Breast cancer is considered invasive and advanced if it reaches stage 3. It has not yet spread to the other organs. This stage is divided into the subsets 3A, 3B, and 3C:

  • In stage 3A, the tumor may be smaller than 2 cm, but there are between four and nine affected lymph nodes. Tumor size at this stage may be larger than 5 cm and involve small gatherings of cells in the lymph nodes. The cancer may have also spread into the lymph nodes in the underarm and breastbone.
  • In stage 3B, the tumor can be any size. At this point, it has also spread into the breastbone or skin and affects up to nine lymph nodes.
  • In stage 3C, the cancer may have spread to over 10 lymph nodes even if no tumor is present. The lymph nodes affected may be near the collarbone, underarm, or breastbone.

Treatment options at stage 3 include:

  • Mastectomy
  • Radiation
  • Hormone therapy
  • Chemotherapy

These treatments are also offered in earlier stages. Your doctor may suggest a combination of treatments for the best outcome.

Stage 4

At stage 4, the breast cancer has metastasized, or spread to other parts of the body. This can include one or more of the following:

  • Brain
  • Bones
  • Lungs
  • Liver

Stage 4 breast cancer is usually considered terminal, but your doctor may try a variety of treatment options to treat the cancer and improve quality and length of life.

Though it is a common disease, breast cancer can be complicated to understand. You can take an active role in your breast cancer care by asking questions and learning about your type of breast cancer, its stage, and the recommended treatments for it.

Speak with one of our dedicated
Alliance Cancer Care team members about

How We
Can Help

Learn More about How We
Can Help


Benefits of Breast Conservation Therapy
October 27, 2023

Benefits of Breast Conservation Therapy

A breast cancer diagnosis can be overwhelming, but with advancements in medical treatments, there are now more options available than ever before. One such option, Breast Conservation Therapy (BCT), offers…

Navigating Breast Cancer Screening
October 20, 2023

Navigating Breast Cancer Screening

October is Breast Cancer Awareness Month, and serves as a reminder of the importance of early detection and proactive health measures. Breast cancer is one of the most common cancers among women, occurring…

Navigating Breast Cancer Treatment: Exploring Modern Radiation Techniques
October 02, 2023

Navigating Breast Cancer Treatment: Exploring Modern…

A breast cancer diagnosis can be an overwhelming experience, but medical treatments continue to evolve, offering advanced treatment options that are both effective and patient-friendly. Modern radiation…

Why Do We Use Chemotherapy with Radiation?
February 01, 2023

Why Do We Use Chemotherapy with Radiation?

By Sarah Joy Patterson-Webb MSN, APRN, AGACNP-BC Your doctors may recommend that you receive chemotherapy while you are receiving radiation treatment. You may see or hear this be called concurrent treatment,…

Seven Things to Know About Getting a Mammogram
January 04, 2023

Seven Things to Know About Getting a Mammogram

In honor of National Breast Cancer Awareness Month, check out this infographic from the American Cancer Society to learn seven things to know about getting a mammogram.  

When should I be screened for breast cancer?
October 05, 2022

When should I be screened for breast cancer?

October is breast cancer awareness month.  Breast cancer is the most common cancer in American women, and it accounts for the second highest number of deaths from cancer in women.  According to the CDC,…

"Being scared, nervous and not knowing what to expect over time there care team was just incredible on a day to day basis. They reassured me. The check-ins were always shined in a positive light which was something that I needed at the time."

- Kristen M.