A diagnosis of breast cancer is only the beginning of understanding the disease. Breast cancers are not all alike, and several pieces of information help determine how serious the cancer is and which treatments are most likely to work.
Among the most important are:
Type: The most common breast cancers begin in the milk ducts or lobules. Some cancers remain confined to where they began, while others have become invasive.
Stage: Describes the size of the cancer and whether it has spread to lymph nodes or other parts of the body.
Grade: Describes how abnormal the cancer cells look and gives clues about how aggressively they may behave.
Hormone receptors: Tests determine whether the cancer is estrogen-receptor (ER) or progesterone-receptor (PR) positive. These cancers may respond to hormone-blocking treatments.
HER2: Some breast cancers produce too much HER2 protein and can be treated with drugs specifically targeting HER2.
Lymph nodes: Whether cancer has reached nearby lymph nodes helps determine the risk that it has spread beyond the breast.
Genomic testing: Tests such as Oncotype DX can sometimes help estimate the likelihood that certain early breast cancers will recur and whether chemotherapy is likely to provide additional benefit.
Inherited genetic testing: In some patients, testing for inherited mutations such as BRCA1 and BRCA2 can affect treatment decisions and provide important information for family members.
These findings are considered together. Two women can both be told they have “breast cancer” yet have very different cancers, treatment choices, and outlooks.
Before deciding on treatment, it is worth understanding exactly what kind of breast cancer you have and which features of the cancer are driving the recommendations.
One of the first things to understand is where the abnormal cells began and whether they have invaded surrounding breast tissue.
Ductal carcinoma in situ (DCIS) consists of abnormal cells confined inside a milk duct. It is often called Stage 0 breast cancer. DCIS is not invasive breast cancer, but some DCIS can eventually develop into invasive cancer. An important controversy is that doctors cannot always predict which cases will progress, raising concerns about overdiagnosis and overtreatment.
Invasive ductal carcinoma (IDC) begins in a milk duct and has spread into surrounding breast tissue. It is the most common type of invasive breast cancer.
Invasive lobular carcinoma (ILC) begins in the milk-producing lobules and has invaded surrounding tissue. It is the second most common invasive breast cancer and can sometimes be more difficult to detect on mammography.
There are also several less common forms of breast cancer.
Knowing whether a cancer is in situ or invasive, ductal or lobular is important, but it is only part of the diagnosis. The cancer's size, grade, lymph-node involvement, hormone-receptor status, HER2 status, and other biological characteristics often have an even greater influence on treatment decisions.
Stage and grade describe different things, and both can help doctors understand a breast cancer and plan treatment.
Stage describes how much cancer is present and how far it has spread. Breast cancer stages range from Stage 0 to Stage IV.
Stage 0 generally refers to DCIS, which remains within the milk ducts.
Stages I and II usually describe cancers confined to the breast or with limited nearby involvement.
Stage III generally describes more extensive cancer in the breast, nearby tissues, or lymph nodes, but without spread to distant organs.
Stage IV, also called metastatic breast cancer, means that the cancer has spread to distant parts of the body, such as the bones, liver, lungs, or brain.
Stage is determined using factors including the size of the tumor, lymph-node involvement, and whether cancer has spread elsewhere. Modern breast cancer staging also takes biological characteristics such as hormone-receptor and HER2 status into account.
Grade is different. A pathologist examines the cancer cells under a microscope and evaluates how different they look from normal breast cells. Grade 1 cancers tend to look more like normal cells and usually grow more slowly. Grade 3 cancers look more abnormal and tend to grow more aggressively. Grade 2 falls between them.
A higher stage does not mean the same thing as a higher grade. Stage tells us primarily where the cancer is and how far it has spread; grade provides information about how the cancer cells are likely to behave.
Both are important, but neither tells the whole story.
Breast cancer cells are routinely tested for certain proteins that can help the cancer grow. These tests are especially important because they can determine which treatments are most likely to work.
Estrogen receptor (ER) and progesterone receptor (PR): Many breast cancers have receptors that allow the hormones estrogen or progesterone to stimulate their growth. These are called hormone-receptor-positive cancers. They can often be treated with drugs that block estrogen or reduce the body's production of estrogen.
HER2: Some breast cancers have unusually high levels of a protein called HER2, which can encourage cancer cells to grow. HER2-positive cancers were once associated with a poorer prognosis, but highly effective HER2-targeted treatments have substantially changed their treatment and outlook.
These tests help divide breast cancers into several important groups:
Hormone-receptor positive, HER2-negative — the most common group; hormone therapy is often an important part of treatment.
HER2-positive — may be hormone-receptor positive or negative and can often be treated with HER2-targeted drugs.
Triple-negative breast cancer — lacks estrogen receptors, progesterone receptors, and excess HER2. Hormone therapy and HER2-targeted drugs therefore do not work against it. Chemotherapy remains important, while immunotherapy and newer targeted treatments are options for some patients.
These biological differences help explain why two breast cancers of the same size and stage may require very different treatments.
Breast cancer can sometimes spread from the breast to nearby lymph nodes, particularly those under the arm. Whether cancer cells are found in these nodes provides important information about the cancer's stage and the likelihood that it could spread elsewhere.
For many women having breast cancer surgery, doctors perform a sentinel lymph node biopsy. The sentinel nodes are the first lymph nodes to which cancer from the breast is most likely to spread. A small number of these nodes can be removed and examined for cancer cells.
If the sentinel nodes are free of cancer, removing many additional lymph nodes can often be avoided. If cancer is found, the significance depends on how much cancer is present, how many nodes are involved, the characteristics of the tumor, and the other treatments being given.
Importantly, finding cancer in nearby lymph nodes does not mean that a woman has metastatic, or Stage IV, breast cancer. Stage IV means that breast cancer has spread to distant parts of the body.
Treatment of the lymph nodes has also become less aggressive for some women. Depending on the circumstances, extensive removal of underarm lymph nodes may not be necessary, helping reduce the risk of lymphedema, shoulder problems, and other complications.
Lymph-node results are therefore an important part of the diagnosis, but they need to be considered together with the tumor's size, stage, grade, hormone-receptor status, HER2 status, and other features.
For some women with early-stage breast cancer, a genomic test can provide information beyond what can be learned from the tumor's size, grade, and appearance under a microscope.
One of the most widely used is Oncotype DX. It examines the activity of 21 genes within the breast cancer itself and produces a Recurrence Score from 0 to 100.
The test is used mainly for certain hormone-receptor-positive, HER2-negative early breast cancers. It can help estimate the likelihood that the cancer will recur and, importantly, whether adding chemotherapy to hormone therapy is likely to provide meaningful additional benefit.
Large studies have shown that many women in this group can safely be treated without chemotherapy. For some women, however, particularly those with higher Recurrence Scores, chemotherapy may provide an important benefit.
The interpretation is not based on the score alone. Age, menopausal status, lymph-node involvement, tumor size and grade, and other clinical factors can affect the decision.
Other genomic tests are also available for selected breast cancers.
These tests should not be confused with inherited genetic tests such as BRCA1 and BRCA2. Genomic tumor tests examine genes within the cancer to help guide treatment. Inherited genetic tests look for mutations a person was born with that may increase cancer risk for that person and family members.
Some breast cancers are related to inherited genetic mutations passed through families. The best known are BRCA1 and BRCA2, but mutations in other genes—including PALB2, CHEK2 and ATM—can also increase breast cancer risk.
Genetic testing may be particularly important for women diagnosed at a younger age, those with triple-negative breast cancer, women with a strong family history of breast, ovarian, pancreatic, or prostate cancer, and women with certain other personal or family cancer histories.
The results can matter for several reasons.
Treatment: Some inherited mutations can affect the choice of breast cancer treatment. For example, certain cancers associated with BRCA mutations may respond to drugs called PARP inhibitors.
Surgery and future risk: A BRCA or other high-risk mutation may increase the risk of developing another breast cancer or certain other cancers and can influence decisions about surgery and future screening.
Family members: Because these mutations can be inherited, a positive result may provide important information for children, siblings, and other relatives, who can then decide whether they want testing themselves.
Genetic testing has expanded considerably, and deciding which genes to test and how to interpret the results can be complicated. Genetic counseling can be valuable both before and after testing.
It is also important to remember that most breast cancers are not caused by an inherited mutation. A negative genetic test therefore does not mean that a breast cancer diagnosis was mistaken or that there is no future risk.
Exactly what type of breast cancer do I have?
What is the stage and grade?
What are my ER, PR, and HER2 results, and what do they mean for treatment?
Are any lymph nodes involved?
Has the cancer spread anywhere beyond the breast and nearby lymph nodes?
Would a genomic test such as Oncotype DX help determine whether I would benefit from chemotherapy?
Should I have inherited genetic testing, such as BRCA1, BRCA2, or other genes?
Are there additional tests that could meaningfully affect my treatment decision?
How quickly do I need to make a treatment decision?
Would getting a second opinion or having my pathology reviewed at another cancer center be useful?
An overview of the tests used to diagnose breast cancer and determine its characteristics.
Clear explanations of pathology reports, breast cancer types, grade, stage, hormone receptors, and HER2 status.
Explains inherited cancer mutations, who may benefit from genetic testing, and the role of genetic counseling.
Information about the genomic test used to help determine whether chemotherapy may benefit certain women with early-stage, hormone-receptor-positive, HER2-negative breast cancer.
An independent patient-advocacy perspective that examines breast cancer screening, diagnosis, and treatment with particular attention to the strength of the evidence, benefits, harms, and areas of controversy.