Breast cancer can develop from a number of cell and tissue types within the breast. Cancer begins as a non-invasive tumor, called a primary tumor, within specific tissues in the breast. If left untreated, the tumor can grow and develop to spread to other organs throughout the body, developing secondary tumors in a process called metastasis. According to Imaginis, breast cancer most commonly metastasizes to the bone, lymph nodes and liver.
Changes to Cells in Primary Tumor
For a tumor to change from a non-invasive tumor to a metastatic cancer, changes occur in a few cells of the tumor. This transition is called the epithelial-mesenchymal transition, also called EMT. In EMT, cancer cells change to take on more stem-cell-like qualities, which gives the cell the capability to give rise to unlimited numbers of cells through cell division to facilitate the development of new tumors. Additionally, the EMT gives the cells migratory abilities, which allows the modified cells to break off from the original tumor and migrate to distant organs to develop secondary tumors. Finally, EMT gives the cells other new properties that help contribute to metastasis.
Only a few cells from a primary tumor need to undergo EMT in order for the cancer to metastasize.
Invading New Tissue
Once cancer cells have migrated away from the primary tumor, they must invade and colonize new tissue in order to begin developing secondary tumors. To do this, the breast cancer cells make a number of proteins referred to as matrix metalloproteases, or MMPs. MMPs help the cell migrate through tissue, until the cells find a spot to grow into a tumor.
In a study published in "Genes and Development," Dr. Kang of Princeton University found that preventing the action of certain MMP proteins has the ability to prevent the development of bone metastases in late-stage breast cancer patients, highlighting the importance of migration and invasion ability in the development of secondary tumors.
Interaction with the New Environment
After invasion and migration into new tissue, the cancer cells must grow and divide to give rise to secondary tumors. To do this, the cancer cells interact with the cells of the healthy tissue and change the environment to support tumor growth. In a 2006 paper published in "Breast Disease," Dr. Tarin reports that cancer cells actively kill neighboring healthy tissue to make room for growth of the secondary tumor. Additionally, the cancer cells recruit blood vessels to provide the nutrients needed for secondary tumor growth.
In cases of metastatic breast cancer, there are often multiple metastases all over the body, most of which are kept dormant and do not form dangerous secondary tumors, highlight the importance of cancer cell-healthy tissue interaction.
