There are many types of breast cancer, and many ways to describe them. One way to differentiate is non-invasive vs. invasive breast cancer, which refers to whether the cancer has spread or not.

Non-invasive or “In situ” breast cancer (ductal carcinoma in situ or DCIS) is a cancer that starts in a milk duct and has not grown into the rest of the breast tissue. Non-invasive cancers stay within the milk ducts or lobules in the breast. They do not grow into or invade normal tissues within or beyond the breast.

Invasive (or infiltrating) breast cancer is any type of breast cancer that has spread (invaded) into the surrounding breast tissue.

Most breast cancers are invasive. Whether the breast cancer is invasive or non-invasive will determine your treatment choices.

About 90% of invasive breast cancers fall into the following types:
•   Invasive ductal carcinoma (IDC). This is the most common type, making up about 80%. With IDC, cancer cells start in a milk duct, break through the walls, and invade breast tissue. It can remain localized, which means it stays near the site where the tumor started. Or cancer cells may spread anywhere in the body.
•   Invasive lobular carcinoma (ILC). This type accounts for about 10% of invasive breast cancers. ILC starts in the lobules or milk glands and then spreads. With ILC, most women feel a thickening instead of a lump in their breast.

In some cases, invasive and non-invasive breast cancer can both be seen in the same specimen. This means that part of the cancer has grown into normal tissue and part of the cancer has stayed inside the milk ducts or milk lobules. It would be treated as an invasive cancer.

A breast cancer also may be a “mixed tumor,” meaning that it contains a mixture of cancerous ductal cells and lobular cells. This type of cancer is also called “invasive mammary breast cancer” or “infiltrating mammary carcinoma.” It would be treated as a ductal carcinoma.

Review this list of signs that may indicate you should see your physician about invasive breast cancer, and be sure to always keep up with your monthly self-exams and regular screenings.