Secondary breast cancer, also known as metastatic breast cancer, is when some of the cancer cells in the breast break away and spread to another part of the body. These cancerous cells then form a new tumor. This is known as secondary breast cancer. The secondary cancer is made up of the same type of cancerous cells as the original cancer within the breast, so even if the cancerous cells create a tumor within the lungs, it is considered secondary breast cancer and not lung cancer.
Secondary breast cancer can affect one part of the body or multiple locations within the body. It can take place either before or after cancer treatment has taken place. The main places where breast cancer cells settle in when spreading are the lymph nodes, liver, bones, lungs and parts of the brain, but it can affect just about anywhere in the body.
There are two ways that breast cancer cells spread to other parts of the body. The first is by penetrating the walls and gaining access to the sites and tissues of the body through the bloodstream, a process known as hematogeneous spread. The other way is by gaining access by penetrating the lymph nodes and spreading through the lymph fluid, a process known as lymphatic spread. After the cancer cells have entered enter into the bloodstream or the lymph fluid, the cells flow down to different organs and tissues, where they get trapped.
Three things can take place after the cells have settled within another location of the body. They can die, they can remain inactive — sometimes for years — or they can grow and divide to form secondary breast cancer. It is not known what causes some cancer cells to stay inactive while others die out, nor is it known what makes these cells form secondary breast cancer. When a person has had breast cancer, the chance of developing secondary breast cancer remains.
The symptoms of this type of cancer can vary based on the areas to which the breast cancer has spread. For example, if the secondary breast cancer is in the bones of one woman, her symptoms will be different from those experienced by a woman whose secondary breast cancer is in her lungs. Therefore, each type of secondary breast cancer does not necessarily have the same symptoms or treatment.