What is cancer?
In a healthy body, natural systems control the creation, growth and death (called apoptosis) of cells. Cancer occurs when these systems do not work right and cells do not die at the normal rate. There is more cell growth than cell death. This excess growth can make a mass of tissue.
What is breast cancer?
Breast cancer occurs when cells in the breast divide and grow without their normal control. Tumors in the breast tend to grow slowly. By the time a lump is large enough to feel, it may have been growing for as long as 10 years. (Some tumors are aggressive and grow much faster.)
Between 50 and 75 percent of breast cancers begin in the milk ducts, 10 to 15 percent begin in the lobules and a few begin in other breast tissues . Learn more about breast anatomy.
It is important to understand the differences between invasive breast cancer and non-invasive breast cancer, called ductal carcinoma in situ (DUK-tul kar-sin-O-ma in SY-too, sometimes called DCIS). These differences affect treatment and prognosis.
Learn more about breast cancer diagnosis, treatment and prognosis.
Invasive breast cancer
Invasive breast cancer occurs when abnormal cells from inside the milk ducts or lobules break out into nearby breast tissue. Cancer cells can travel from the breast to other parts of the body through the blood stream or the lymphatic system. They may travel early in the process when the tumor is small or later when the tumor is large.
The lymph nodes in the underarm area (the axillary lymph nodes) are the first place breast cancer is likely to spread. In advanced stages, breast cancer cells may spread to other parts of the body like the liver, lungs, bones and brain (a process called metastasis). There, the breast cancer cells may again begin to divide too quickly and make new tumors.
Non-invasive breast cancer - ductal carcinoma in situ (DCIS)
When abnormal cells grow inside the milk ducts, but have not spread to nearby tissue or beyond, the condition is called ductal carcinoma in situ (DCIS). The term "in situ" means "in place." With DCIS, the abnormal cells are still "in place" inside the ducts. DCIS is a non-invasive breast cancer (you may also hear the term “pre-invasive breast carcinoma”).
Although the abnormal cells have not spread to tissues outside the ducts, they can develop into invasive breast cancer. Learn more about DCIS and the risk of invasive breast cancer.
Learn about treatment for DCIS.
Breast cancer in men
Breast cancer in men is rare, but it does happen. Learn more about breast cancer in men.