The two main categories of breast cancer are invasive and noninvasive. Noninvasive breast cancers stay within the milk ducts and lobules (milk-producing glands) of the breast. Most breast cancers are invasive. They spread beyond these areas and invade healthy tissue.

The most common noninvasive type of breast cancer is ductal carcinoma in situ (DCIS), in which cancer develops in the ducts that carry milk to the nipple but does not spread beyond those ducts.

A similar condition, lobular carcinoma in situ, begins in the lobules and does not grow any further. Unlike DCIS, LCIS is not considered a cancer, but if you have it, you have a higher risk of developing breast cancer.

Invasive Ductal Carcinoma: The Most Common Type of Breast Cancer

The most common form of breast cancer is invasive ductal carcinoma (IDC), sometimes also called infiltrating ductal carcinoma. About 80 percent of all breast cancers are IDC, and the risk of getting IDC increases as you grow older.

IDC starts in the ducts just as DCIS does but then grows beyond the ducts and invades the surrounding healthy tissue inside the breast. Without treatment, the cancer can metastasize, or spread, into the lymph nodes and other areas of the body.

The options available to treat IDC depend in part on the stage of the cancer, as well as other factors, including the grade of the cancer.

Breast Cancer Stages: What Do They Mean?

Stages are numbers used to describe how far a cancer has advanced and where it has spread in the body. Cancer that has not spread beyond the breast is considered local.

Regional cancer has spread into the lymph nodes, mostly those in the armpit. When cancer spreads to other parts of the body, it is considered distant, since it exists far away from the breasts.

Your prognosis, or your long-term outcome, relies heavily on what stage your cancer is. Cancer stages are often broken down further into subcategories to provide more specific information.

Staging previously relied only on the size of the tumor and whether it had grown into surrounding tissue, whether the cancer was in the lymph nodes, and whether it had spread to other parts of the body beyond the breast.

Breast cancer stages now also take into account the tumor’s grade (how much the cancer cells resemble healthy cells); the cancer’s estrogen receptor, progesterone receptor, and HER2 status; and the Oncotype DX score, which means the cancer is estrogen-receptor positive, HER2 negative, and there is no cancer in the lymph nodes.

Estrogen receptor, progesterone receptor, and HER2 status all have to do with the specific hormones or proteins involved in the cancer.

Breast Cancer Stages: From 0 to 4

Breast cancer, like most cancers, has four stages, plus stage 0.

Stage 0 refers to noninvasive breast cancers, such as DCIS.

Stage 1 cancer is invasive and spreading beyond where it started.

In stage 1A, the cancer is 2 centimeters (cm) or smaller and has not spread into the lymph nodes or outside of the breast.

In stage 1B, small clumps of cancer cells ranging from 0.2 to 2 millimeters (mm) exist in the lymph nodes. There may not be a tumor in the breast, but if there is, it measures no bigger than 2 cm.

Stage 2 cancer also has two subcategories. Stage 2A describes a cancer that has spread to one to three lymph nodes under your arms (axillary lymph nodes), with or without a tumor up to 2 cm large in the breast; or the breast tumor measures 2 to 5 cm, and there are no cancer cells in the axillary lymph nodes.

Stage 2B refers to a tumor between 2 and 5 cm combined with cancer in the lymph nodes (small groups of cancer cells between 0.2 and 2 mm or cancer in one to three axillary lymph nodes or lymph nodes near the breastbone), or the tumor is larger than 5 cm, but no cancer exists in the axillary lymph nodes.

Stage 3 breast cancer includes stages 3A, 3B, and 3C. In stage 3A, the tumor may be any size and has spread to four to nine lymph nodes close to the breastbone or in the axilla. The tumor may also be larger than 5 cm with small clumps of breast cancer cells that have spread to one to three axillary lymph nodes or nodes near the breast bone.

In stage 3B, the tumor (any size) has reached the skin of your breast or chest wall and caused swelling or an ulcer, and the cancer may have spread to up to nine lymph nodes under your arms or near your breastbone.

Inflammatory breast cancer is automatically stage 3B or a later stage. Inflammatory breast cancer typically includes reddening of a large area of the breast skin, the breast feels warm and may be swollen, and cancer cells have spread to the lymph nodes and may be found in the skin.

In stage 3C, the cancer may be any size and has spread to the chest wall or breast skin, as in stage 3B; or it has spread to 10 or more axillary lymph nodes, to lymph nodes above or below your collarbone, or to axillary lymph nodes and those near your breastbone.

Stage 4 breast cancer, also called metastatic breast cancer (MBC), has spread beyond the breast and lymph nodes to other areas in the body. Breast cancer is typically considered incurable at stage 4, but therapies can help treat it so that you can manage it and live for years.

Median survival rates after diagnosis with MBC have continued to increase, especially for women diagnosed at younger ages.

Tumor Grades: How the Cells Look

The tumor grade, sometimes called the cell grade, is a scale of G1 to G3 that classifies how abnormal the cancer cells look under a microscope.

Cells in grade 1 tumors look only a little bit different than healthy cells and grow slowly, and not many new cancer cells are forming. Grade 2 cells don’t resemble healthy cells and are growing and dividing a little bit faster than normal. Grade 3 cells look very different than healthy cells and grow quickly, with many new cancer cells forming.

In addition to your cancer’s stage and the tumor’s grade, other factors that affect your prognosis include the type of breast cancer you have, the hormones or proteins involved, and how quickly tumor cells are dividing and the tumor is growing.

Editorial Sources and Fact-Checking

Noninvasive or Invasive Breast Cancer. BreastCancer.org. September 21, 2020.

Invasive Ductal Carcinoma (IDC). BreastCancer.org. March 9, 2019.

Breast Cancer Stages. BreastCancer.org. May 11, 2021.

Mariotto A, Etzioni R, Hurlbert M, et al. Estimation of the Number of Women Living With Metastatic Breast Cancer in the United States. Cancer Epidemiology, Biomarkers & Prevention. June 2017.

Cell Grade. BreastCancer.org. September 21, 2020.

Factors That Affect Prognosis and Treatment. Susan G. Komen. November 15, 2021.

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