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 that it can be divided into five stages:
- Invasion and infiltration of underlying tissues by cancer cells due to permeation of small lymphatic and blood vessels;
- Release of these cancer cells into the lymphatic and/or blood circulation, single and/or in the form of small emboli;
- Survival of such cancerous cells in the lymphatic and/or blood circulation;
- Retention in the capillary beds of distant organs;
- Extravasation of the lymphatic and/or blood vessels with the growth of the disseminated cancer cells.
It is important to emphasize that metastases are always formed from malignant tumors – benign neoplasms do not generate metastasis.
When the metastasis occurs in lymph nodes, tissues, or organs close to the primary site (place in the body where the cancer originated), it is called regional metastasis. If the secondary tumor formation is in organs or tissues far from the cancer’s starting point, it is called distant metastasis.
Most common types of metastatic cancer
Under microscopic analysis, it is possible to define which cell type forms the malignant tumor being diagnosed.
Metastatic cancer is characterized by cancerous cells from the primary organ in a different organ – for example: breast cancer cells in the liver set up metastatic breast cancer in the liver (and not liver cancer).
If the cells detected in the second occurrence of cancer are from the organ itself – for example, liver cancer cells in the liver, after there has been breast cancer in the same body – this is a patient who has had two primary cancers, not one metastasis.
The most frequent sites of metastasis according to the origin of the primary tumor:
- Breast, pancreatic, thyroid, and kidney cancer: metastasize to liver, lungs, and bones;
- Lung cancer: to liver, bones, pleura, and brain;
- Bladder cancer: metastasizes to retroperitoneal lymph nodes;
- Stomach cancer and colorectal cancer: regional lymph nodes;
- Melanoma: metastasis to the brain;
- Ovarian Cancer: peritoneum;
- Prostate cancer: bones;
- Uterine cancer: peritoneum and regional lymph nodes.
Symptoms of metastasis
Like primary cancers, metastasis can be asymptomatic in many cases. When symptoms manifest themselves depends on the size and location of the metastatic tumors.
The main symptoms of metastasis are similar to the signs of primary tumors:
- Body aches and pains;
- Bone fractures (when metastases affect the bones);
- Persistent headache;
- Shortness of breath
- Weight loss for no apparent reason
- Changes in urinary or bowel function.
Diagnosis of metastasis
Metastasis is usually diagnosed during follow-up examinations of the patient after the end of treatment for primary cancer. The tests that detect it most often are imaging tests, such as X-ray, CT scan, MRI, and PET scan.
Changes in blood test results can also raise the suspicion of metastasis – these changes indicate the presence of proteins that are released when there is cancer and when there is metastasis.
Treatment of Metastasis
Treatment of metastasis should follow the protocols of the original cancer, rather than where the tumor is installed secondarily. For example: metastatic breast cancer in the liver should be treated with the same therapies as breast cancer, not liver cancer.
Surgery is only done if the metastasis is compressing or impairing the function of a contiguous organ. The most common treatment options for metastasis, which can be used alone or in combination, are chemotherapy, hormone therapy, immunotherapy, and radiation therapy.
Prevention of metastasis
Early detection of primary cancer is the most effective way to prevent the formation of metastasis. When the cancer is removed in its early stages, the risk that it will release daughter cells into the circulation, with the ability to spread to other sites in the body, is much lower.