Understanding breast cancer: types, stages and tests

What breast cancer is, what hormone receptors and HER2 mean, how stage and grade are described, and the tests you may have, in plain language.

6 min read · last reviewed September 30, 2026

After a breast cancer diagnosis, you will hear a lot of new words: receptors, HER2, grade, stage. It can feel like learning a new language in a week. The good news is that each of these words gives your team useful information. Together they point to the treatments most likely to work for you.

Here is a plain-language guide to what your diagnosis means.

What is breast cancer?

Your body is made of tiny cells that grow and divide in an orderly way. Cancer happens when some cells start to grow out of control and form a lump called a tumour.

Most breast cancers start in the milk ducts (the tubes that carry milk to the nipple) or in the lobules (the glands that make milk). Breast cancer can sometimes spread to the lymph nodes under the arm, and less often to other parts of the body.

Breast cancer is much more common in women, but men can get it too. Men have a small amount of breast tissue, and most of what you read here applies to them as well.

Non-invasive or invasive?

DCIS (ductal carcinoma in situ) means abnormal cells are found only inside the milk ducts. They have not grown into the nearby breast tissue. DCIS is sometimes called "stage 0" or pre-invasive breast cancer. It is usually treated to stop it from turning into invasive cancer.

Invasive breast cancer has grown beyond the ducts or lobules into the breast tissue around them. The most common kinds are invasive ductal carcinoma (also called "no special type") and invasive lobular carcinoma.

The labels that guide treatment

When the cancer is tested in the lab, your team looks for certain proteins on the cancer cells. These are some of the most important results on your pathology report.

Hormone receptor-positive (ER-positive and/or PR-positive). These cancers have receptors for the hormones estrogen or progesterone. The hormones act like fuel and help the cancer grow. This is the most common type. The good news is that hormone (endocrine) therapy can block that fuel.

HER2-positive. HER2 is a protein that helps cells grow. Some cancers make too much of it, which can make them grow faster. Medicines that target HER2 work very well for these cancers. A HER2-positive cancer can also be hormone receptor-positive.

Triple-negative. These cancers have no estrogen or progesterone receptors and do not make extra HER2. Hormone therapy and standard HER2 medicines don't work for them, so chemotherapy is the main treatment. Immunotherapy and other newer medicines also help some people.

HER2-low. This is a newer label for cancers with a small amount of HER2, not enough to be called HER2-positive. For some people with advanced cancer, it can open the door to a newer type of medicine. Ask your team whether this label applies to you.

Grade: how the cells look

Grade describes how different the cancer cells look from normal cells under a microscope.

• Grade 1 (low grade): cells look a lot like normal cells and tend to grow slowly.
• Grade 2 (intermediate grade): in between.
• Grade 3 (high grade): cells look very different from normal cells and tend to grow faster.

A higher grade does not mean treatment won't work. It helps your team decide how strong a treatment you may need.

Stage: how big and how far

Stage describes the size of the cancer and whether it has spread. Doctors use the "TNM" system: T for the tumour, N for the lymph nodes, and M for metastasis (spread to distant parts of the body). They also add in the grade and receptor results. In plain words:

• Stage 0: DCIS. Abnormal cells are only inside the ducts.
• Stage 1: a small cancer, with no spread or only tiny amounts in nearby lymph nodes.
• Stage 2: a larger cancer, or one that has spread to a few lymph nodes under the arm.
• Stage 3: a cancer that is larger or has reached more lymph nodes, the skin or the chest wall. This is often called locally advanced.
• Stage 4: the cancer has spread to other parts of the body, such as the bones, liver or lungs. This is also called metastatic breast cancer. It can't usually be removed completely, but it can often be treated and controlled for a long time.

Your stage may not be final until after surgery, when the tumour and lymph nodes can be checked in the lab.

Something you can do: Ask for a copy of your pathology report. Ask your team to circle the results that matter most and explain them.

Tests you may have

Imaging. A mammogram (an X-ray of the breast) and a breast ultrasound are often the first tests. Some people also have a breast MRI. If there's a chance the cancer has spread, you may have a CT scan, bone scan or PET scan.

Core needle biopsy. A doctor uses a hollow needle to take small samples of tissue after numbing the area. This is the only way to confirm cancer. The same samples are tested for hormone receptors and HER2.

Sentinel lymph node biopsy. During surgery, the surgeon finds and removes the first few lymph nodes the cancer would drain to. If they are clear, more nodes usually don't need to be removed.

Genomic tests. For some hormone receptor-positive cancers, a lab test looks at a group of genes in the tumour. It gives a "recurrence score" that helps show who is likely to benefit from chemotherapy and who can safely skip it.

Genetic testing. A blood or saliva test can check for inherited gene changes, such as in the BRCA1 or BRCA2 genes. It may be offered based on your age, your cancer type or your family history. The result can guide your treatment and may matter for your relatives too.

Something you can do: Before each test, ask, "What will this test tell us, and when will I get the results?"

Questions to ask your care team

• Is my cancer DCIS or invasive? What type is it?
• Is my cancer hormone receptor-positive, HER2-positive or triple-negative? What does that mean for my treatment?
• What is the grade and stage of my cancer?
• Do I need more tests before we make a plan?
• Would a genomic test or genetic testing help me?
• Can I have a copy of my pathology report?

This article is general information, not medical advice. Talk with your health care team about your own situation. In an emergency, call 9-1-1 or your local emergency number.

In an emergency, call 9-1-1 or your local emergency number.

General information, not medical advice. It does not replace your own care team. If you think you or someone else is having a medical emergency, call 9-1-1 or your local emergency number. If you are in crisis or thinking about suicide, call or text 9-8-8 (Canada and the US).

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