The most serious pattern of breast cancer spread is through the blood stream to involve different organs in the body.
Metastatic disease is most often the mechanism by which breast cancer becomes life-threatening.
Once they have entered the circulatory system, they can travel to almost any site in the body. Common sites of breast cancer metastases include the bone or skeletal system, the lungs, the liver, and the brain. Most women diagnosed with breast cancer will have a chest X-ray and blood tests to screen for the presence of metastatic disease. Unfortunately, even if these tests are normal, a patient continues to have a risk that metastatic disease may become detectable later. This is because tumors first spread to other organs with a relatively low number of cells.