What is Metastasis
Metastasis is the formation of a secondary tumor from a primary cancerous lesion in another part of the body, without anatomical continuity between the two parts.
This spread of cancer throughout the body is not fully understood, but it is known to occur in five stages:
- Invasion and infiltration of underlying tissues by cancer cells, due to the permeation of small lymphatic and blood vessels;
- Release of these cancer cells into the lymphatic and/or bloodstream, either individually or in the form of small emboli;
- Survival of these cancer cells in the lymphatic and/or bloodstream;
- Lodging in the capillary beds of distant organs;
- Extravasation from the lymphatic and/or bloodstream with growth of disseminated cancer cells.
It is important to note that metastases always arise from malignant tumors – benign neoplasms do not metastasize.
When metastasis occurs in the lymph nodes, tissues, or organs near the primary site (the location in the body where the cancer originated), it is called regional metastasis. If the formation of the secondary tumor is in organs or tissues distant from the initial site of cancer, it is called distant metastasis.
Most common types of metastatic cancer
Under microscopic analysis, it is possible to determine the type of cell forming the malignant tumor to be diagnosed.
Metastatic cancer is characterized by cancer cells from the primary organ in a different organ – for example: breast cancer cells in the liver constitute metastatic breast cancer in the liver (and not liver cancer).
If the cells detected in a second occurrence of cancer are from the same organ – for example, liver cancer cells in the liver, after there has been breast cancer in that same body – it is a patient who had two primary cancers, not metastasis.
The most frequent sites of metastases according to the origin of the primary tumor:
- Breast, pancreas, thyroid, and kidney cancer: metastasis to the liver, lung, and bones;
- Lung cancer: to the liver, bones, pleura, and brain;
- Bladder cancer: metastases in retroperitoneal lymph nodes;
- Stomach and colorectal cancer: regional lymph nodes;
- Melanoma: metastases to the brain;
- Ovarian cancer: peritoneum;
- Prostate cancer: bones;
- Uterine cancer: peritoneum and regional lymph nodes.
Symptoms of metastases
Just like primary cancers, metastasis can be asymptomatic in many cases. When symptoms do occur, they depend on the size and location of the metastatic tumors.
The main symptoms of metastasis are similar to the signs of primary tumors:
- Body aches;
- Bone fractures (when metastases affect the bones);
- Persistent headache;
- Dizziness;
- Seizures;
- Shortness of breath;
- Fever;
- Unexplained weight loss;
- Changes in urinary or bowel function.
Diagnosis of metastasis
Metastasis (when cancer spreads throughout the body) is usually diagnosed during follow-up exams after the completion of treatment for a primary cancer. Imaging tests such as X-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI), and PET scans are often used to detect it.
Changes in blood test results can also raise suspicion of metastasis, as these changes indicate the presence of proteins that are released when cancer or metastasis is present.
Treatment of metastasis
The treatment of metastasis should follow the protocols of the original cancer, not the location where the tumor is installed secondarily. For example, a metastatic breast cancer in the liver should be treated with the same therapies as breast cancer, not liver cancer.
Surgery is only performed if the metastasis is compressing or impairing the function of a contiguous organ. The most common treatment options for metastases, which can be used alone or in combination, are chemotherapy, hormonal therapy, immunotherapy, and radiotherapy.
Prevention of metastasis
Early detection of the primary cancer is the most effective way to prevent the formation of metastasis. When cancer is removed in its early stages, the risk of it releasing daughter cells into the circulation, with the ability to spread to other parts of the body, is much lower.
