When breast cancer is diagnosed, it’s given a grade and a stage. These different but related classifications help oncologists predict how aggressive a cancer may be. This information is crucial in determining which breast cancer treatment plans are likely to be the most effective.

Grading and staging measure different aspects of a cancer tumor. The breast cancer tumor (and possibly one or more lymph nodes) will be biopsied — a bit of breast tissue will be removed and analyzed in the laboratory — and the doctor may also order imaging tests. The tumor’s grade and stage will be determined based on the results.

Keep reading to learn more about how staging and grading for breast cancer provide different details about your breast cancer, helping you and your cancer care team make informed decisions about your treatment options.

Grading and Staging Help Determine Prognosis

A prognosis for breast cancer is a forecast of how serious the disease is, how it’s likely to proceed, and how many years the person will likely survive. Oncologists assess an individual’s prognosis by considering the grade, stage, and type of breast cancer, along with other relevant factors. They then calculate the prognosis based on how thousands of similar cases have progressed and responded to treatment. Other factors such as an individual’s age, overall health, and response to treatment can also affect a prognosis for breast cancer.

Generally, a higher stage and grade mean a poorer prognosis. More advanced stages are harder to treat. However, treatment options are expanding for each stage of breast cancer.

Grade Is Based on How Breast Cancer Cells Look

The grade of a tumor refers to how different breast cancer cells appear compared to normal, healthy cells when viewed under a microscope. This information is written on a pathology report. Cancer tumors are generally graded on a scale of 1 to 4, although different scales may be used for different types of breast cancer. The higher the grade, the more abnormal the cancer cells appear. A higher grade indicates the cancer will probably be more aggressive. Standard grading includes:

• Grade 1 — Cancer cells look similar to normal cells.
• Grade 2 — More abnormal cancer cells are detected.
• Grade 3 — Cancer cells are abnormal overall.
• Grade 4 — Cancer cells are highly abnormal.

Tumor grade refers to how different breast cancer cells appear compared to normal, healthy cells when viewed under a microscope.

For noninvasive breast cancers such as ductal carcinoma in situ (DCIS), a three-level grading scale is often used to describe the appearance of the cancer cell’s nucleus. DCIS cells are classified as low-, intermediate, or high-grade (nuclear grade 1, 2, or 3). Low-grade DCIS cells generally resemble normal cells more closely and tend to grow more slowly, while high-grade DCIS cells look abnormal and grow faster.

Staging Is Based on Grade Plus Other Breast Cancer Details

To stage breast cancer, doctors consider the grade of the cancer cells as well as details about the size of the tumor, where breast cancer has spread, and whether cancer cells have certain genetic mutations (variants) and proteins.

Before 2018, breast cancer was staged according to the TNM staging system, which measured the following:

• The size of the primary tumor, also known as the original tumor (T)
• The number of lymph nodes to which the cancer has spread (N)
• The presence of metastasis, meaning the cancer has spread to other parts of the body such as the lungs, brain, bones, or liver (M)

Doctors stage breast cancer based on the grade, the size of the tumor, where cancer has spread, and other details.

Upgraded Staging of Breast Cancer

In recent years, breast cancer staging has become more detailed, improving accuracy. Additional details help doctors better predict how the cancer will progress and determine the most effective treatment.

In 2018, the American Joint Committee on Cancer published new standards for staging breast cancer. In addition to the TNM system, which measures tumor size and cancer spread, the updated staging now includes tumor grade and biomarker testing — genetic testing of cancer cells for hormone receptors like estrogen and progesterone, human epidermal growth factor receptor 2 (HER2), and other mutations and proteins.

Breast cancer staging involves a complex analysis of everything that can influence how a tumor may grow and spread. Even though two individuals may have the same type of breast cancer with similar tumors, their staging may differ, depending on the grade of the cancer cells and any biomarkers.

Genetic Testing, Staging, and Breast Cancer Subtypes

Genetic tests for cancer cells, such as the Oncotype DX Breast Recurrence Score, MammaPrint test, and Prosigna, are sometimes used in staging. These tests look at a set of genes in the cancer cells. For example, Oncotype DX evaluates 21 genes that are linked to breast cancer. The score can help oncologists determine if the cancer is likely to recur (relapse, or return after treatment).

Genetic testing gives oncology researchers a better understanding of subtypes of breast cancer tumors. For instance, depending on hormone receptor status, doctors can determine whether hormone therapy may be an appropriate treatment option. Some treatments can block overproduction of HER2, a protein that can cause cancer cells to grow faster.

Other Tests That May Affect Breast Cancer Staging

Several other imaging and laboratory tests may be used when staging breast cancer. These include:

• Sentinel lymph node biopsy, which looks at the first axillary lymph node, where breast cancer is most likely to spread
• Chest X-ray
• Computed tomography (CT) scan
• Positron emission tomography (PET) scan
• Magnetic resonance imaging (MRI)
• Bone scan
• Blood tests to measure organ function

Stages of Breast Cancer

If you’re diagnosed with breast cancer, your oncologist will assign a stage number, usually ranging from 1 to 4. Cancer stages are sometimes noted with Roman numerals, as stages I through IV. Some cases of very early breast cancer are considered stage 0. Here are some general guidelines for the stages of breast cancer.

Stage 0

Breast cancer is sometimes referred to as stage 0 when there’s no sign of cancer spreading beyond the tissue it started in. Stage 0 breast cancer is considered noninvasive or preinvasive. Some abnormal cells look like cancer cells, but they haven’t spread to other healthy breast tissue.

When breast cancer is diagnosed, doctors give it a stage from 0 to 4. Stage 0 cancer hasn’t spread at all, while stage 4 has spread to different parts of the body.

Stage 0 is also referred to as carcinoma in situ. It can be difficult to detect stage 0 breast cancer because it often doesn’t have obvious symptoms. Stage 0 breast cancer is typically discovered in a routine mammogram or another imaging test.

Stage 0 breast cancer is very treatable when it’s detected early.

Stage 1

In stage 1 breast cancer, tumor cells have spread to nearby tissue or lymph nodes, but the cancer is still only in a small area. Stage 1 is considered early-stage invasive breast cancer.

Stage 1 breast cancer is categorized as stage 1A or 1B. In stage 1A, the tumor is less than 20 millimeters in diameter — about the size of a grape — and no cancer cells are found in the lymph nodes.

In stage 1B, either the tumor is less than 20 millimeters and there are cancer cells in the lymph nodes, or no tumor is detected but tiny groups of cancer cells (less than 2 millimeters) are found in the lymph nodes. Stage 1B breast cancer that is estrogen receptor-positive or progesterone receptor-positive may be reclassified as stage 1A because it’s considered less aggressive.

Stage 1 breast cancer is considered early, localized cancer and is usually very treatable.

Stage 2

Stage 2 breast cancer is an invasive cancer that’s classified as stage 2A or 2B. The exact classification depends on the size of the tumor, lymph node involvement, tumor grade, and other factors, such as whether it’s hormone receptor-positive or HER2-positive. In stage 2 breast cancer, there may not be a detectable tumor in the breast itself if cancer larger than 2 millimeters is found in nearby lymph nodes, such as those in the armpit or near the breastbone.

Breast cancer that might otherwise be considered stage 2 might be classified as stage 1 depending on its hormone receptor status, HER2 status, and Oncotype DX Recurrence Score.

Stage 2 breast cancer requires a more aggressive treatment approach that can last three to 18 months or more. If cancer cells are estrogen receptor-positive, hormone therapy may be given for five to 10 years.

Stage 3

Stage 3 breast cancer is an invasive cancer that’s classified stage 3A, 3B, or 3C. The exact staging is based on the size of the tumor, the spread of the cancer, its tumor grade, and specific hormone receptor and HER2 characteristics of the cancer cells. Stage 3 breast cancers have spread to the lymph nodes.

Stage 3B breast cancer has generally spread to the skin of the breast or chest wall and causes swelling or an ulcer (wound). When the breast becomes red and swollen, the condition is known as inflammatory breast cancer and may be classified as stage 3C. More widespread lymph node involvement also may be staged as 3C.

For stage 3 breast cancer, doctors may recommend treatment with a complete mastectomy (removal of the entire breast) and other therapies. In some cases, chemotherapy may shrink the tumor, and the cancer will be treated with a lumpectomy (breast-preserving surgery). Lymph node removal and radiation are also frequently recommended for stage 3 breast cancers.

Stage 4

Stage 4 breast cancer is advanced, late-stage cancer. In stage 4, cancer cells have metastasized — spread to other parts of the body such as the liver, lungs, brain, or bones or to distant lymph nodes. Between 6 percent and 10 percent of women are initially diagnosed with stage 4 breast cancer, according to the Breast Cancer Research Foundation. From 20 percent to 30 percent of breast cancer cases develop into stage 4 cancer.

Life expectancy for people with stage 4 metastatic breast cancer is improving. With newer treatment, more stage 4 cases can be managed like chronic conditions. People with estrogen receptor-positive, progesterone receptor-positive, and HER2-negative breast cancers now have more treatment options, thanks to a new class of drugs.

Talk to Your Doctor About Breast Cancer Grading and Staging

If you have questions about how your breast cancer has been graded or staged, be sure to talk with your cancer care team. Your doctor can explain how the grading of your breast cancer tumor may have affected your cancer staging.

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