Learn more about breast cancer

After skin cancer, breast cancer is the second-most commonly diagnosed cancer among U.S. women, affecting one in eight women who live to the age of 80. An estimated 313,510 new cases of breast cancer will be diagnosed in U.S. women in 2024, according to the American Cancer Society. Breast cancer accounts for 15 percent of all new cancer diagnoses and 7 percent of all cancer deaths each year.

Breast cancer develops when cells in the breast mutate and grow out of control, forming a tumor. Exactly what causes breast cells to mutate isn’t known, but certain factors can increase the risk of this happening. Aging and genetics are the biggest contributors to a woman’s breast cancer risk.

Breast cancers share one main thing in common—they all begin in the breast. Most breast cancers start in the ducts that carry milk to the nipple, or in the “lobules,” where breast milk is made. However, there are many differenttypes of breast cancer, and the distinctions between them can be difficult to understand.

Breast cancer types are separated into two main groups: invasive or in situ (noninvasive). All types of breast cancer fall under one of these categories.

In situ (non-invasive): When breast cancer is not invasive, it is most likely ductal carcinoma in situ (DCIS), a noninvasive type of breast cancer that starts in a milk duct and has not yet spread anywhere else. DCIS accounts for approximately 1 in 5 new cases of breast cancer. DCIS is also called stage 0 breast cancer, and most women have a positive prognosis at this stage. However, DCIS can progress and spread beyond the milk ducts, becoming invasive cancer.

Invasive: Invasive breast cancer refers to any breast cancer that spreads from the original site and “invades” other areas, like nearby breast tissue, lymph nodes or anywhere else in the body. Most breast cancers are invasive.

The most common type of invasive breast cancer is called invasive ductal carcinoma (IDC). IDC accounts for roughly 70 to 80 percent of all breast cancers. IDC starts in a milk duct and spreads, growing into other parts of the breast. With time, it may spread further, or metastasize, to other parts of the body.

Invasive lobular carcinoma (ILC) is the second-most common type, accounting for roughly 5 to 10 percent of all breast cancers. ILC starts in lobules—where breast milk is made—and then spreads into nearby breast tissue. Like IDC, it can metastasize.

There are many other subtypes of invasive breast cancer—some are more challenging to treat or easier to treat than the more common IDC.

The stage of cancer is one of the most important factors in evaluating your treatment options.

The American Joint Committee on Cancer developed the TNM cancer staging system to evaluate three primary factors when it comes to treating cancer—T, N and M:

Tumor (T) describes the size of the original tumor.

Node (N) indicates whether cancer was found in the lymph nodes.

Metastasis (M) refers to whether cancer has spread to other parts of the body.

These three elements (TNM) correspond to one of five stages, numbered between stage 0 and stage 4. In general, the higher the stage, the more advanced the cancer.

Stage 0

This is early cancer detected only in the layer of cells in which it began (also called carcinoma in situ).

Stages 1, 2 or 3

The higher the stage number, the larger a tumor may have grown or the more extensively the cancer may have spread, either to nearby lymph nodes and/or organs near the primary tumor.

Stage 4

The cancer has spread to other areas of the body.

Recurrent

In recurrent cancer, the disease has returned after treatment.