Breast cancer appears when one or more cells of the breast grow and multiply abnormally. This anomalous growth can form a nodule (extra mass of cells), also known as tumor.

Degenerating cells normally belong to one of two structures in the mammary gland : the lobules or the mammary ducts.

They normally cover and protect these structures, but, following a number of errors/changes in their genetic material (mutations), they instead grow into a tumor or neoplasm (neo=new +plasm =growth). Many times these tumors are benign (or NON-cancerous).

A new tissue is not in itself a problem as long as its growth is limited. This is often the case with benign tumors.

In malignant tumors, though, not only do the cells divide without control, but they also develop the ability to move and invade other tissues (this process is called metastasis). This spreads the cancer to remote places in the body. Benign tumors, on the other hand, remain where they first emerged (their cells are never mobile).

An ability to move is one of the more important differences between malignant and benign tumors.

In breast cancer, the most common targets for metastasis are the lungs, liver, brain or bones, with the cancer cells reaching them through the lymphatic and the blood system. 

There is, however, one “non-invasive” type of breast cancer called carcinoma ductal in situ (CDIS), where the cancer cells remain in the milk ducts. Although CDIS is not life threatening, it can evolve into invasive cancer, so it is important that is detected early and removed.

Learn more about the most common cancer among women worldwide: localization in the body and geographic distribution  , as well as the different types of breast tumors and their classification .

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