• Breast cancer has five stages indicating how severe the cancer is and how much it has spread.
• Stage 0 breast cancer is the least severe whereas stage IV is usually the most concerning.
• Staging breast cancer helps doctors communicate the severity of the condition and choose treatment.

Breast cancer is categorized into five stages, from zero to four. Generally, stage zero is the least concerning and stage four is the most severe, where the cancer has grown and spread.

Related Article Module: Follow this 5-step guide to check for breast cancer at home

In the US, women have a 1 in 8 chance of developing breast cancer, according to the American Cancer Society. But fortunately, breast cancer is usually diagnosed as stage I, "because we use mammograms and other imaging tools to diagnose it before a lot of women are even aware that they have something going on," says Norah Lynn Henry, MD, breast oncology disease lead at the Rogel Cancer Center at the University of Michigan.

But in other countries where this type of technology is not as common, breast cancer is diagnosed at a higher stage, she says.

Why breast cancer is staged

Breast cancer stages are used to guide therapy, says Yolanda Bryce, MD, a radiologist at Memorial Sloan Kettering Cancer Center. They help oncologists communicate about and help patients understand the type and severity of cancer they have, Henry says.

Different stages have different survival rates, but it's important not to get too hung up on the statistics, because situations vary depending on the individual, Bryce says.

"There's so much innovation and so much advancement in the field that [a patient's] clinical picture doesn't necessarily look like the published numbers," she says.

How quickly breast cancer progresses from one stage to the next varies widely. Some cancers can take a few months to progress, and others can take years, Bryce says.

Here's a guide on the different stages of breast cancer and what each stage may mean for you.

Stage 0 breast cancer

Stage 0 is the earliest stage of breast cancer, also called ductal carcinoma in situ (DCIS).

It refers to cancer that is present in the milk duct but has not spread outside of the ducts or lobules into the surrounding breast tissue.

You can think of it like little flecks of cancer that haven't formed into a tumor yet, Bryce says. In stage 0, you typically have no symptoms - you can't see or feel a mass yet, she says.

For stage 0, the five-year survival rate, meaning the percent of people who live at least five years after the cancer is found, is 100%.

Stage I breast cancer

In Stage I, the cancer cells have spread to surrounding breast tissue, but they are still contained in a small area. Stage I is divided into stages IA and IB.

In stage IA:

• The tumor measures up to 20 millimeters (mm).
• Cancer has not spread to the lymph nodes.

In stage IB:

• No tumor or a small tumor (less than 20 mm) is in the breast.
• Small clusters of cancer cells are in the lymph nodes.

Many people with stage I cancer have no symptoms, but some women feel a mass, Henry says. "For most women, it's found on [a] mammogram," she says.

The five-year survival rate is 98% to 100% for stage I. Because cancer caught at this stage has a high survival rate, this underscores the importance of getting mammograms, Bryce says. And a sizable number of women do not.

In 2018, an estimated 63% of US women 45 and older were up to date with breast cancer screening, according to a 2021 American Cancer Society report.

Stage II breast cancer

In stage II breast cancer, the cancer has grown larger but is still in a limited region of the breast. Like stage I, stage II is broken up into two substages:

Stage IIA involves one of the following:

• There is no tumor or a small tumor (up to 20 mm) in the breast, plus cancer has spread to the lymph nodes under the arm.
• Or there is a tumor of 20 to 50 mm in the breast, but cancer has not spread to the lymph nodes.

Stage IIB involves one of the following:

• A tumor of 20 to 50 mm is in the breast, and cancer has spread to between one and three nearby lymph nodes.
• Or the tumor is larger than 50 mm, but cancer has not spread to any lymph nodes.

Women with stage II breast cancer often feel a mass in their breast, and if they have more cancer in their lymph nodes, they may feel a mass under their arm, Henry says. But they still may not feel anything. Other possible symptoms include:

• Thickening or swelling of part of the breast
• Irritated, dimpled, red, or flaky skin on the breast
• Pulling in or inversion of the nipple
• Nipple discharge other than breast milk, sometimes bloody
• Any change in the size or the shape of the breast
• Pain in the breast

Although pain may be a symptom, it's not common, Bryce says.

The five-year survival rate for stage II is 90-99%.

Stage III breast cancer

In stage III, the cancer has spread farther in the breast, or the tumor is larger. This stage includes three subcategories:

Stage IIIA involves one of the following:

• Cancer is found in four to nine nearby lymph nodes, with or without a tumor in the breast.
• A breast tumor is larger than 50 mm, and the cancer has spread to between one and three nearby lymph nodes.

In stage IIIB, the tumor has spread to the chest wall behind the breast, and:

• Cancer may have spread to the skin, causing swelling or inflammation.
• Cancer may have broken through the skin, causing a wound.
• Cancer may have spread to as many as nine lymph nodes under the arm or nodes near the breastbone.

In stage IIIC, with or without a tumor in the breast, the cancer has spread to one of the following places:

• Ten or more underarm lymph nodes
• Lymph nodes near the collarbone
• Some underarm lymph nodes and lymph nodes near the breastbone
• The skin of the breast

In stage III, the patient may experience similar symptoms as stage II, listed earlier. The five-year survival rate for stage III breast cancer is 66% to 98%.

Note: For stages 0 to III, the goal is to cure the cancer and to keep it from coming back, Henry says. "The higher the stage, the more likely the cancer is to come back."

Stage IV breast cancer

Stage IV, also called metastatic, is the most advanced stage of breast cancer. In this stage, the cancer has spread to nearby lymph nodes and to other parts of the body, such as the lungs, liver, brain, or bones.

If the cancer has spread to the bone, patients may have bone pain or back pain, and if it has spread to the liver, patients may have pain on the right side of their abdomen, Bryce says. Some of the changes in the skin and nipple listed earlier under stage II may also occur in stage IV.

When the cancer has spread to other, distant parts of the body, the five-year survival rate is 28%. "With the treatments that we have available to us today, most patients, unfortunately, are not cured of their cancer" if it is stage IV, Henry says. But, she adds, "We can still treat, we can still manage, we can still help people feel good for as long as possible."

Also, many new treatments are emerging. "People are living longer even with stage IV disease," Bryce says. A 2018 study found that the effectiveness of breast cancer treatment on survival increased substantially from 1975 to 2015.

Other information about staging

Along with the numerical stages, breast cancer is classified using the American Joint Committee on Cancer TNM system, which takes into account:

• The size of the tumor (T),
• Spread to nearby lymph nodes (N),
• Spread or metastasis to distant sites (M),
• Estrogen receptor (ER) status,
• Progesterone receptor (PR) status,
• Status called Her2 protein (Her2),
• The grade of the cancer (G), or how much the cells look like normal cells

"The grade for breast cancer is how aggressive it looks under the microscope," Henry says. The grade is also assigned a number, with one being the least aggressive and three being the most. Since both the stage and grade are numbered systems, patients sometimes confuse the two, she says.

When meeting with a breast cancer patient, Henry says she talks about the stage, the grade, and other factors to advise the best form of treatment.

Insider's takeaway

Breast cancer is classified into five different stages, in part to make it easier for health care providers and patients to communicate about and understand the type of cancer.

"Usually, the most common presentation is nothing. You don't feel anything at all. And I think it's important to stress that that's why mammogram is necessary," Bryce says.

If you've been diagnosed with breast cancer, don't be afraid to ask your oncologist questions, Henry says. Patients may not fully understand the risks and benefits of a treatment, especially "in the stress and the overwhelming nature of first getting diagnosed with cancer," she says.

For other sources of information on breast cancer, Henry recommends the American Society of Clinical Oncology's cancer.net and Susan G. Komen's breast cancer website.

How to recognize the signs and symptoms of breast cancer, according to OB-GYNsYes, men can get breast cancer - here are the symptoms to watch forDense breasts increase the risk of breast cancer - here's how to tell if you're among the 50% of people who have themHow to treat vaginismus through dilation training and counseling