Breast cancer begins when healthy cells in the breast change and grow out of control. The cells that grow out of control form a mass of cells called a tumor. A tumor can be benign or malignant. Malignant is when it grows and spreads to other parts of the body, and benign is when it grows and does not spread.

Although breast cancer most often spreads to nearby lymph nodes, breast cancer is still considered a local disease. It can spread throughout the body through the blood vessels or lymph nodes to places such as the bones, lungs, liver, and brain. This is called metastatic or stage 4 breast cancer, although involvement of only nearby lymph nodes is usually not stage 4 breast cancer.

Breast cancer statistics

In 2020, there were 2,261,419 new cases of breast cancer among women worldwide. In 2023, in the United States, an estimated 297,790 women will be diagnosed with invasive breast cancer, and 55,720 women will be diagnosed with non-invasive breast cancer. Since the mid-2000s, invasive breast cancer in women has increased by about half a percent each year. 

Currently, 4 million women in the United States have breast cancer. Breast cancer is the fifth leading cause of death among women worldwide. In 2020, 684,996 women worldwide died from breast cancer.

Breast cancer is usually diagnosed in middle-aged and older women. The average age of diagnosis is 63 years. Although it is not common, some women are diagnosed with the disease before the age of 45.

Breast cancer survival rate

There are different types of statistics that help doctors estimate the chances of being cured of breast cancer, called survival statistics. It is important to note that survival statistics for people with breast cancer are only estimates. In the United States, the five-year relative survival rate for women with nonmetastatic invasive breast cancer is 911%, and the ten-year relative survival rate is 851%. Breast cancer survival rates vary and depend on several factors, including the stage of the cancer, the person's age, and their general health.

If invasive breast cancer is confined to the breast, the five-year relative survival rate for women with this disease is 99%. Approximately 61% of women have cancer that has spread outside the breast and lymph nodes.