Common Types of Breast Cancer

Invasive (infiltrating) ductal carcinoma is the most common type of breast cancer.   This type starts in a milk duct, then breaks through the wall of the duct and grows into, or invades, the neighboring  breast tissue.  At this point, cancer cells can travel though the bloodstream or lymphatic system to the lymph nodes as well as other parts of the body.  Approximately 80% of invasive breast cancers are infiltrating ductal carcinomas.

Invasive (infiltrating) lobular carcinoma is the second most common type of invasive breast cancer, accounting for up to 15% of invasive cancers.  This type starts in the milk-producing glands, the lobules.

Ductal carcinoma in situ (DCIS) is an early or pre-invasive form of breast cancer that is being diagnosed at an increasing rate due to the implementation of screening mammography.  Unlike invasive breast cancer, the tumor cells in DCIS are confined to the milk ducts within the breast and have not spread through the walls of the ducts to surrounding breast tissue.  Thus, they do not have the ability spread to the lymph nodes or systemic circulation.  Even though DCIS is not invasive, it is still considered a form of breast cancer and is treated similarly to invasive cancer: with surgery, plus or minus the addition of radiation (depending on the type of surgery you undergo).

Lobular carcinoma in situ (LCIS) is thought of as a "risk indicator of cancer," but not a true cancer.  Most experts believe that LCIS seldom progresses to invasive cancer.  However, women with this condition do have a higher risk of developing an invasive breast cancer in the same or opposite breast, with an overall 8 to 12 fold greater lifetime risk compared to the general population.

Next: Less Common Types of Breast Cancer.