Definition and Overview
Metastatic disease, also known simply as metastasis, refers to a cancer or disease that has spread from one organ to another part of the body that is not directly connected to the original source of the disease. The new cancers caused are each called metastases, coming from a Greek word that means “displacement.” Once a primary cancer metastasizes, the resulting tumour is called the secondary cancer. This is possible with any form of cancer, including blood and lymphatic cancers. The most common sites of metastasis are the bones, liver, and lungs.
Causes of Condition
Metastatic disease develops when cancer cells penetrate through the blood vessels or the lymphatic system, making their way into the body’s blood circulation. Dubbed as intravasation or circulation, these are the two most common cause of metastatic disease that forms in a distant location. However, if the location is closer to the original source, it is caused by a local invasion.
For metastases to occur, cancer cells first have to break away from the original tumour, enter the lymphatic system or bloodstream, travel to another body part, and penetrate through the blood or lymph vessel to access a new organ. Once there, they need to grow depending on the location. For this to occur, they need to withstand the attacks of the body’s immune system. If abnormal cells are able to go through all these steps, they will be able to successfully form tumours. This means that the possibility of metastases formation still depends on individual conditions, including the state of the immune system in the secondary location. Thus, researchers focusing on metastatic disease are trying to find not just new ways to treat the condition, but also ways on how to disrupt the metastatic process.
Not all cancer cells that are able to travel to another part of the body cause disease. It is possible for the abnormal cells to lie dormant in the secondary location without growing. However, if a new tumour is indeed formed, the metastasized cells remain similar in composition with the original tumour cells. This means that even if lung cancer metastasizes to the breasts, the metastatic breast tumour will be made up of malignant lung cells and will still be considered as lung cancer instead of breast cancer.
While most cancers commonly metastasize to the bone, liver, and lungs, different types of primary cancers tend to metastasize to specific body parts. Here are the common types of cancer and their common sites of metastases:
- Breast cancer – Brain
- Colorectal cancer – Peritoneum
- Kidney – Brain, adrenal gland
- Lung – Other lung, brain, adrenal gland
- Melanoma – Brain, skin, muscle
- Ovary – Peritoneum
- Pancreas – Peritoneum
- Prostate – Adrenal gland
- Stomach – Peritoneum
- Uterus – Peritoneum, vagina
In many cases of metastatic disease, the patients did not experience any symptoms relating to the secondary cancer site. More often than not, metastases are only found on x-rays and other common tests conducted on cancer patients.
If symptoms are present, however, they will usually affect the secondary organ. Thus, the symptoms tend to differ.
Metastatic brain disease usually cause:
- Loss of balance
Metastatic lung disease is often accompanied by:
- Chest pain
- Shortness of breath
The symptoms of metastatic liver disease include:
- Abdominal swelling
Who to See and Types of Treatment Available
Since metastatic is just a re-occurrence of an existing disease, it is not difficult for patients to seek medical help. Most of the time, cancer patients are already working with cancer specialists called oncologists, who specialize in the diagnosis and treatment of cancer. These oncologists will still be the patient’s primary care provider for the metastatic disease.
The treatment for metastatic disease will be based on the treatment of the original cancer. Thus, for lung cancer that has spread to the breasts, the doctor will prescribe treatments that are known to be effective against metastatic lung cancer, instead of treatments for breast cancer. However, since the cells that form secondary tumours may not be exactly the same as the original tumour, this makes metastatic cancer more challenging to treat despite the availability of treatment.
However, there are cases where the metastatic disease has already begun its formation even before the original cancer is found. In such cases, patients who are experiencing symptoms can go to their general physician or family doctor for a physical exam. If cancer is suspected or detected, the patient will be referred to an oncologist or cancer specialist.
There are also instances where the metastatic disease is found first, before the original tumour is even detected. This poses a serious challenge during treatment, especially if the abnormal cells have managed to spread to several places, making it difficult to determine the primary tumour. Another similar challenge is when a metastatic disease is found but there is no trace of the original cancer, either because it is too small or has already regressed. While it is easy to detect that the abnormal cells in the secondary site are only metastasized cells, it is harder to identify their primary origin. Such cases are treated differently and are called as cancers with unknown primary origin (CUP). However, due to recent advances in diagnostic techniques, the rate of CUPs has significantly declined.
The goals of treating metastatic disease are to:
- Control further metastases
- Control the growth of both the primary and secondary tumours
- Relieve the symptoms experienced by the patient
The common treatment methods used for metastatic disease include the following techniques, or a combination of them:
- Biological therapy
- Targeted therapy
- Hormonal therapy
- Radiation therapy
The choice of treatment ultimately depends on the type of cancer, the patient’s previous cancer treatments, the size and quantity of the tumour, and the patient’s age and general health condition.
So far, treatment for metastatic disease is helpful in prolonging patients’ lives. Unfortunately, there is still a long way to go in the development of these treatments, as many patients who eventually die of cancer actually die due to metastatic disease instead of the original disease.
National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines): Hepatobiliary cancers. Version 2.2014. Available at http://nccn.org/professionals/physician_gls/pdf/hepatobiliary.pdf. Accessed April 10, 2014
Sherman KL, Mahvi DM. Liver metastases. In: Niederhuber JE, Armitage JO, Doroshow JH, et al., eds. Abeloff's Clinical Oncology. 5th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2013:chap 53