One of the reasons I started this site was to help patients become more informed about their diagnosis. Pathologists and other breast care professionals use a variety of terms and phrases for breast cancer that can be confusing and sometimes seem contradictory. The best definition for breast cancer is an invasive carcinoma. Carcinoma refers to a cancer made up of epithelium, the cells that line the major organs of the body. This is a tumor where the cancer cells have spread outside the confines of the ducts and lobules into the surrounding breast tissue. These tumors have the ability to spread (metastasize) to other parts of the body.

The terms ductal carcinoma in situ and lobular carcinoma in situ are even more confusing. While most doctors believe a cancer is an uncontrolled growth that can spread, then adding the phrase in situ, which means non-invasive, seems contradictory. However, based upon most of the research in this area, most doctors believe ductal carcinoma in situ IS a cancer because, in some cases, the cells have the capability to invade the surrounding breast tissue and become an invasive carcinoma later on. This is sometimes refered to as a “precursor” lesion.

Lobular carcinoma in situ is another story. Most doctors do not believe lobular carcinoma in situ is a true cancer but rather a risk factor for developing invasive cancer at a later point in life. This is based upon research that showed that lobular carcinoma in situ does not behave as a “precursor” lesion like ductal carcinoma in situ. However, more recent studies are questioning this idea and hopefully more research on lobular carcinoma in situ will help us better understand how it behaves. But for now, lobular carcinoma in situ is not treated like ductal carcinoma in situ.

© 2008-2010 Seattle Breast Pathology Consultants, LLC. All rights reserved.