Metastatic cancer is a cancer that spreads from a primary site to another body part. The process of spreading of cancer cells from one part of the body to another is called metastasis. All cancers if not treated can develop metastatic cancers. In fact most cancer patients die due to metastatic cancer. For instance, breast cancer patients only die of metastatic breast cancer, often in the lung. Treatment of metastatic cancer is difficult and the survival rate for patients with metastatic cancer is low.
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Spread of cancer in the body can occur by transport of cancer cells in the blood stream and transport of cancer cells in the lymphatic system. At the new locations, some cancer cells will survive, continue to growth and divide and form colony tumours. The new tumours will share similar characteristics to the original tumour. For instance, metastatic colon cancer cells in the liver will look similar to cancer cells in the colon under microscope.
Each cancer has different routes of developing metastatic cancers. The most common metastatic cancers for colorectal cancer are in lung and liver. For breast cancers, the most common metastatic sites are in the liver, bone, brain and lung.
Some patients with metastatic cancers are asymptomatic. For other, the symptoms vary according the sites of metastatic cancers. Metastatic cancers in bones often cause a lot of pain and in some cases, bone fractures. Metastatic cancer in the brain can cause headaches and seizures. Patients with lung metastases may suffer from shortness of breath. Metastatic cancers can also be found early through x-ray and diagnostic tests. In some cases, metastatic cancers are found before diagnoses of primary tumours. Pathologists can tell whether a cancer is metastatic or primary based on comparing the cancer cells to the cells in the tissue where the cancer is located. In patients with advanced cancers, metastatic cancers are often found together the primary tumour.
Metastatic cancer is responsible for most cancer deaths. Interestingly, most primary tumours originate in non-vital organs that can be surgically removed for instance in the breast, colon, lung and prostate. If the cancer is localised, surgery is sufficient. However, if the cancer metastasises to vital organs such as brain, it will disrupt normal function of these organs and lead to serious consequences. Thus, the presence of metastatic cancer significantly lowers the chance of survival for cancer patients. For instance, the average 5-year survival of patients with colorectal cancer is 50%. However, in patients with liver or lung metastases, the 5-year survival rate is only 25%.
It should be noted here some cancers are fatal without metastases, like leukaemia or brain cancer.
Treatment of metastatic cancers include radiation therapy, hormone therapy, surgery, chemotherapy and biologic therapy. In practice, treatment of metastatic cancers often involves a combination of 2 or 3 treatment modalities. Oncologists recommend treatments based on characteristics of the primary cancer, and location and size of metastatic cancers. Patient's health and age are also taken into account since most of the above treatment methods have serious side-effects.
Treatment of metastatic cancer has evolved rapidly in the past two decades. For instance, for five decades, from the 1950s to the 1990s, treatment of metastatic colorectal cancer had been primarily based on 5-fluorouracil (5-FU). However, with the introduction of irinotecan and oxaliplatin at the end of 1990s and recent FDA approval of use of biologics (e.g. bevacizumab, cetuximab) as adjuvant therapy, the survival rate of patients with metastatic colorectal cancer has been greatly improved.