How Does Breast Cancer Spread?

The primary tumor starts in the breast itself. However, once activated, it can progress beyond the breast to regional lymph nodes. Therefore, it can reach other organs or systems in the body. (does not metastasize) Lymph is a clear, protein-rich fluid that removes metabolic wastes or dead cells from the body. Lymph will return to the bloodstream via tiny channels known as lymphatics. Along the way, it is filtered through cellular stations called lymph nodes. That is why it is called a lymph node. Almost all organs in the body have a primary group of lymph nodes that filter lymph. In the breast, the primary lymph nodes are in the armpit. Classically, the primary tumor begins in the breast. The most likely place to spread is the regional lymph nodes. Cancer can also enter blood vessels in a rapid invading action. If cancer enters the blood vessels, the blood vessels provide another pathway for the cancer to spread to other organs of the body.

Although breast cancer follows this classical progression, it often becomes systemic or diffuse during the course of the disease. When a person can feel a lump in the breast, it is usually one centimeter in size. The resulting tumor contains roughly one million cells. It is estimated that a tumor of this size can take one to five years to develop. During this time, the cancer can metastasize and spread to other parts of the body by lymphatics or blood.

When primary breast cancer spreads, it may first travel to the regional lymph nodes in the armpit. In this case, there is regional metastasis. If it spreads rapidly and progresses elsewhere through the lymphatic system or blood, it develops systemic metastases that can involve numerous other organs in the body. Common sites of systemic spread for breast cancer are the lung, bones, liver, skin, and soft tissues. As it turned out, the presence and actual number of regional lymph nodes containing cancer is the best indicator of whether the cancer is widely metastatic. Since tests to detect metastases in other organs may not be sensitive enough to reveal tiny deposits, evaluation for regional metastasis is very important in making treatment decisions for this disease. If breast cancer spreads to other important organs of the body, its presence compromises the function of these organs. Death can occur as a result of excessive decline in the function of vital organs.