Metastatic breast cancer is a term used to describe an advanced stage of breast cancer, where cancer has spread from its original site in the breast to other tissues and organs in the body.
Phases of metastasis
The various phases of metastasis include:
- First, malignant cells break away from the primary tumour and penetrate the surrounding extracellular matrix which separates the tumour from other tissues.
- Next, the cancer may enter blood vessels and spread to all the majorly perfused organs (those with a rich blood supply) such as the liver, kidney, bones and brain. This spread through the blood vessels is called hematogenous spread.
- The cancer may also enter the lymphatic system and travel along lymph channels to other parts of the body (lymphatic spread).
- Whether the cancer spreads via blood or lymph channels, cancer cells eventually reach vital organs where they then begin to grow. The sites most commonly targeted by breast cancer cells are the lung, liver, bones and brain.
Aims of treatment
Metastatic breast cancer is often a very advanced stage of breast cancer where the likelihood of treating the cancer and achieving long-term survival are less than if the cancer had been diagnosed at an earlier stage. Women with this stage of disease often have a lower 5-year survival rate than women with early-stage breast cancers. Treatment aims for women with this aggressive and widely spread cancer include:
- Prolong life for as much as possible
- Reduce symptoms
- Maintain or improve quality of life
Treatment depends on several factors including:
- Location of the metastasis
- Number of sites affected with metastasis
- Aggressiveness of the metastasis
- General health, age and ability of the patient to withstand rigorous cancer therapy
- Early treatment failures and successes
- Severity of symptoms
Treatments offered include:
- Hormone therapy - This is suitable for women with cancer that tests positive for the estrogen receptor (ER+), a receptor that can be targeted and blocked to prevent the growth of estrogen-dependent cancers. Even if the cancer has spread to distant parts of the body, it may shrink in response to hormonal therapy which therefore forms the mainstay of treatment at this stage. One well known drug of this class is Tamoxifen. The adverse side effects of such drugs are less than with traditional cancer-killing chemotherapy because the agents target only the ER positive tissues in the body, while sparing others.
- Biological targeted therapy - These agents target a specific cell surface receptor that is abundant in some tumours, called the human epidermal growth factor receptor 2 (HER2 receptor). Breast cancer cells with more than two copies of the HER2 gene display more of the HER2 protein on their surface and these cells can be targeted with agents such as trastuzumab (Herceptin). Herceptin can bind to the HER2 present on primary tumour cells as well as metastasized cancer cells. These agents however may be used only in individuals who have a cancer that is HER2-positive.
- Chemotherapy with traditional cancer chemotherapy drugs - These are suitable for those who do not have ER positive cancer. The chemotherapy agents can stop the growth of a tumour and kill the cancer cells to reduce breast cancer symptoms. A combination of chemotherapy agents is commonly used.
- Radiation therapy may be given as a palliative measure to kill cancer cells and ease the symptoms of advanced cancer that has spread to distant organs. This is used in cases where cancer has spread to the bones.
- Surgery is rarely used in metastatic breast cancer, mainly because the cancer has already spread to distant organs and surgery fails to remove all the cancer cells. It may however be used as a palliative therapy to ease the burden of the symptoms of advanced cancer.
- Pain relief and palliative care - These may be employed to reduce symptoms and ease pain.