The most advanced stage of breast cancer is stage 4 breast cancer, also called metastatic breast cancer. Metastasis occurs when cancer cells of the original tumor in the breast spread to other parts of the body. Once metastasis has occurred, intensive treatment is required to achieve the best possible outcome.
To determine the best treatment options, a doctor will typically investigate the following information in addition to the stage of disease:
In stage 4 breast cancer, the cancer has metastasized (spread) to distant tissues such as the lungs, bone, brain, or liver. A variety of tests are used to look for metastases. Among them are bone scans to detect bone metastases and imaging techniques — like X-rays, computed tomography (CT) scans, or positron emission tomography (PET) scans — to examine other organs.
Metastatic disease is the primary factor distinguishing stage 4 breast cancer from early-stage breast cancer. The breast tumor can be any size and the lymph nodes may or may not contain cancer cells.
As with other stages of breast cancer, stage 4 breast cancer is sometimes referred to with Roman numerals, i.e., “stage IV breast cancer.”
Unlike earlier stages of breast cancer, surgery is not typically used to treat metastatic breast cancer. Rather, systemic therapy that affects the entire body, including chemotherapy and drug therapy, is the standard approach. The most effective treatment options depend on important genetic features of the cancer. Due to the widespread nature of the disease, stage 4 breast cancer treatments can continue until the cancer starts to show resistance, responds completely, or the side effects become intolerable.
Metastatic breast cancer is often initially treated using chemotherapy to selectively kill cancer cells in the body. Many drugs and drug combinations may be used in chemotherapy regimens to treat stage 4 breast cancer.
Estrogen receptors and progesterone receptors are types of proteins called hormone receptors, which play a role in breast cancer progression. Hormone receptor-positive stage 4 breast cancers can be treated with hormone therapy drugs like tamoxifen or exemestane (Aromasin), which specifically target the function of hormone receptors.
Targeted drugs work by stopping the function of a particular protein or group of proteins. Drugs like trastuzumab (Herceptin) are effective against breast cancers that contain the HER2 protein. Combined with chemotherapy, trastuzumab has been shown to greatly improve the survival of those with HER2-positive cancers, according to a 2014 study from the Journal of Clinical Oncology.
For HER2-negative cancers, other drugs such as the PARP inhibitor olaparib (Lynparza) may be administered following chemotherapy. Another targeted drug called palbociclib (Ibrance) is part of a class of drugs called kinase inhibitors. This drug may be used to treat stage 4 breast cancers that are HER2-negative but ER-positive.
It is now more common for metastatic breast cancer to go into complete remission, meaning all signs and symptoms disappear. Maintenance therapy may then be given, to keep cancer in remission.
Immunotherapy is a newer type of drug therapy that uses a person’s immune system to help it recognize and fight cancer cells. This form of treatment is effective against triple-negative breast cancer, a treatment-resistant type of breast cancer that is negative for ER, PR, and HER2. Several immunotherapy drugs are available for treating triple-negative breast cancer.
While generally not the primary treatment option for metastatic breast cancer, local treatments such as surgery and radiation therapy may be used in some cases. Possible applications include treatment of central nervous system metastases, prevention of bone fractures, and pain relief.
Since stage 4 breast cancer is spread throughout the body at the time of diagnosis, unfortunately it has a generally poor prognosis (outlook). In the United States, about 33 percent of women diagnosed with metastatic breast cancer live five or more years after diagnosis, according to Susan G. Komen, and some women now can live 10 or more years beyond diagnosis. There are also marked differences across racial and ethnic groups, with Black women having lower survival relative to white women.
Although there is still much room for improvement, there’s been significant progress in identifying effective treatments for metastatic breast cancer, leading to longer survival times and improved quality of life for many people. Continued participation in clinical trials can advance the discovery of more effective therapies and lead to improved outcomes for stage 4 breast cancer.
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