Breast cancer is a type of cancer where cells in the breast divide and grow without normal control. Between 50 and 75 percent of breast cancers begin in the ducts, 10 to 15 percent begin in the lobules and a few begin in other breast tissues [4].

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. However, some tumors are aggressive and grow much more rapidly.

It is important to understand the difference between invasive breast cancer and non-invasive breast cancer, called ductal carcinoma in situ (kar-sin-O-ma in SY-too).

Learn breast cancer diagnosis and treatment.

Invasive breast cancer

Invasive breast cancer occurs when abnormal cells from inside the ducts or lobules break out into nearby breast tissue. This allows the cancer cells to spread to the lymph nodes and, in advanced stages, to organs like the liver, lungs and bones (a process called metastasis). 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.

Ductal carcinoma in situ (DCIS, non-invasive breast cancer)

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

Both men and women can get breast cancer. Learn more about male breast cancer.

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