The breasts contain lymph vessels. These vessels lead to small, round organs called lymph nodes. Groups of lymph nodes are near the breast in the axilla (underarm), above the collarbone, in the chest behind the breastbone, and in many other parts of the body. The lymph nodes trap bacteria, cancer cells, or other harmful substances.

Cancer begins in cells, the building blocks that make up tissues. Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, they die, and new cells take their place. Sometimes, this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor.

Tumors can be benign or malignant. Malignant tumors are the ones that cause cancer. While these tumors can be removed, they also have the potential to grow back and spread. When breast cancer cells spread, the cancer cells are often found in lymph nodes near the breast. Breast cancer can also spread to almost any other part of the body. The most common areas for the cancer to spread are the bones, liver, lungs, and brain. The new tumor has the same kind of abnormal cells and the same name as the original tumor. For example, if breast cancer spreads to the bones, the cancer cells in the bones are actually breast cancer cells. The disease is metastatic breast cancer, not bone cancer. For that reason, it is treated as breast cancer, not bone cancer. Doctors call the new tumor "distant" or metastatic disease.

If you have been wrongfully diagnosed with breast cancer, it is important to seek legal advice, as you may have cause for a medical malpractice claim.