Metastases are secondary tumor lesions that form from the primary tumor. However, the primary tumor and metastases are not in direct anatomic contact. Every malignant tumor has a potential to form metastases after it reaches certain size (certain number of tumor cells). It is not the rule but the majority of tumors do not spread by metastases until having the diameter of about one centimeter.
Many tumors spread by blood and lymphatic vessels. The lymphatic spread is usually the first allowing the tumor to invade local lymph nodes and later by blood to affect distant organs and tissues. The presence of enlarged lymph nodes or distant organ metastases significantly worsens the prognosis and changes the treatment strategy. Some tumors tend to form metastases in specific locations (such as colon cancer) but others are totally unpredictable and can form metastases “anytime and anywhere” (e.g. kidney cancer, melanoma).
There is also a term “micrometastases”. Micrometastases are small metastases, whose size makes them undetectable by standard imaging methods. If the primary tumor is large, the presence of micrometastases is probable and that is the reason of a post-operative chemotherapy, which is intended to destroy those micrometastases. (More details can be found in text dedicated to malignant tumors). We usually seek metastases in these organs:
Liver metastases are very common as tumors of the digestive tract and gynecological tumors metastasize to liver. Substantial amount of blood flows through the liver tissue and this makes liver very sensitive to metastatic spread. Liver metastases may be asymptomatic, but sometimes they cause enlargement of the liver, abdominal pain in the right upper quadrant or even direct disorders of liver functions – liver failure manifesting with jaundice, impaired blood clotting, etc.
Brain metastases may have a very dramatic manifestation. They can cause epileptic seizures, personality changes, sensitive disorders and muscle paralysis. Metastases can also lead to brain swelling and intracranial bleeding resulting in intracranial hypertension and symptoms such as headache, nausea, vomiting and unconsciousness. Brain metastases are very difficult to treat, but in certain indications they can be successfully destroyed by Leksell gamma knife.
Bone metastases are very annoying. Tumors quite usually affect the vertebrae but every single bone can be invaded by the tumor cells. Some metastases are osteoblastic and others are osteolytic. Osteoblastic metastases cause excessive local production of bone; osteolytic metastases cause destruction of bone tissue. The result is similar – bone pain and increased risk of pathologic fractures. The therapy is usually only symptomatic – radiotherapy of the metastases brings a distinctive pain relief. Bisphosphonates (drugs blocking the bone decalcification) may be used against the osteolytic metastases.
Note: Tumors coming from blood cells (leukemias and lymphomas) spread by blood to a number of tissues (lymph nodes, liver, spleen, etc.). There is no clear primary tumor and so we do not talk about metastases.
The shema shows a malignant tumor of the intestine,
local metastases in lymph nodes and distant metastases in the liver.
If we find a malignant tumor in the body, we usually search for the presence of metastases. Physical examination allows us to find enlarged liver, spleen and enlarged subcutaneous lymph nodes. Deeper tissues may be examined by imaging methods such as chest X-ray, abdominal ultrasound, computed tomography or magnetic resonance imaging. In some cases, we can use scintigraphy (such as bone scintigraphy to find bone metastases) and PET-CT examination.
The opposite situation occurs when we find a suspected metastasis and we want to know its source. Sometimes, this is a very challenging task. If possible, it is advisable to obtain a tissue sample from the suspected metastasis to confirm its malignant etiology and histological structure to estimate the type of primary tumor.
Tumor metastases are usually treated by chemotherapy, bone metastases are irradiated. In some exceptional cases, metastases may be removed surgically. More detailed information can be found in text dedicated to treatment of cancer.