The American Cancer Society estimate that in 2017, there were over 310,000 new cases of breast cancer among American women.

Of these, 63,410 women had breast cancer in situ and 252,710 had invasive breast cancer.

In situ breast cancer, also called ductal carcinoma in situ, is a non-invasive form of breast cancer in which the cancer cells that line the milk ducts have not broken through the walls of the ducts and have not managed to spread to the surrounding breast tissue.

In invasive breast cancer, on the other hand, which is also called infiltrating breast cancer, cancer cells have spread beyond the ducts and can migrate through the blood and lymphatic system to other parts of the body.

To distinguish clearly between non-invasive and invasive breast cancer, physicians look at the so-called myoepithelial layer — a layer of cells surrounding those that line the interior of the milk ducts.

When cancer cells have managed to break through this layer, doctors give a diagnosis of invasive breast cancer — a form of breast cancer that is more difficult to treat.

Now, new research shows that the myoepithelial layer is not just a passive "fortress" that may or may not be invaded by cancer cells. The myoepithelium actively tries to reach out and snatch the cancer cells that are trying to escape to the rest of the body.

The new study was led by Andrew Ewald, who is a professor of cell biology at the Johns Hopkins University School of Medicine in Baltimore, MD, and the findings were published in the Journal of Cell Biology.

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