What Is Breast Cancer? PDF, 144KB
Anatomy of Breast Cancer - Updated: Invasive Carcinoma
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Breast cancer is a type of cancer where cells in the breast divide and grow without normal control. About 85 percent of breast cancers begin in the mammary ducts, while about 15 percent arise in the lobules [3]. 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 can be aggressive, and grow much more rapidly.
It is important to understand the difference between invasive cancer and ductal carcinoma in situ (kar-sin-O-ma in SY-too). These are discussed below and you can find more in the Diagnosis and Treatment sections.
Invasive Breast Cancer
Invasive breast cancer occurs when abnormal cells from inside the lobules or ducts 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 in a process called metastasis.
Breast cancer may grow from a tiny tumor to a larger one, later traveling to nearby lymph nodes, then distant ones. Finally, it may spread in other parts of the body. Cancer cells can also travel from the breast through the blood and lymphatic system early in the process when the tumor is small [4].
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 cancer. For more on DCIS and risk of invasive breast cancer, visit the Risk Factors section. For treatment information, visit Ductal Carcinoma in Situ.
Both men and women can get breast cancer. For more on male breast health, see Breast Facts for Men.
Updated 10/19/09
