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Metastatic cancer is a cancer that has spread from the part of the body where it started, which is the primary site, to other parts of the body. Even when cancer has spread to a new area, it's still named after the part of the body where it started. For example, if prostate cancer spreads to the bones, it's still prostate cancer (not bone cancer). Likewise, breast cancer that has spread to the lungs is still breast cancer, not lung cancer, and is treated as metastatic breast cancer.
Picture: This image shows some parts of the lymph system, like lymph nodes and lymph vessels, as well as organs and tissues that contain many lymphocytes (immune cells)
Where a cancer starts often plays a role in where it will spread. Most cancer cells that break free from the original tumor are carried in the bloodstream or lymph system until they get trapped in the next "downstream" organ or set of lymph nodes. Once the cells are there, they can start new tumors. When cancer does spread to other organs and start to form new tumors, it's because of certain genetic changes in the cells. Cancer cells often break away from the main (primary) tumor and travel through the blood and/or lymph system, but they don't always settle in and start new tumors. Most of the time, the cells that broke away die. When cancer does spread to other organs and start to form new tumors, it's because of certain genetic changes in the cells.
Cancer cells grow out of control and become invasive and are less specialized than normal cells. Non-cancer cells mature into very distinct cell types with specific functions, cancer cells on the other hand do not. Cancer cells continue to divide without stopping due to the lack of function. In addition, cancer cells are able to ignore signals that normally tell cells to stop dividing. Cancer cells also may be able to influence the normal cells, molecules, and blood vessels that surround them and feed a tumor. For instance, cancer cells can induce nearby normal cells to form blood vessels that supply tumors with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumors.
During the early stages of cancer, tumors are typically benign and remain confined within the normal boundaries of a tissue. As tumors grow and become malignant, however, they gain the ability to break through these boundaries and invade adjoining tissues.
Invasive cancer cells often secrete proteases, which is an enzyme that breaks down protein into its building blocks, amino acids that enable them to degrade the extracellular matrix at a tissue's boundary. Proteases also give cancer cells the ability to create new passageways in tissues. For example, they can break down the junctions that join cells together, thereby gaining access to new territories.
These are the most common sites of cancer metastasis.
Cancer cell metastasis usually involves the following steps:
Local invasion: Cancer cells invade nearby normal tissue.
Intravasation: Cancer cells invade and move through the walls of nearby lymph vessels orblood vessels.
Circulation: Cancer cells move through the lymphatic system and the bloodstream to other parts of the body.
Arrest and extravasation: Cancer cells arrest, or stop moving, in small blood vessels called capillaries at a distant location. They then invade the walls of the capillaries and migrate into the surrounding tissue (extravasation).
Proliferation: Cancer cells multiply at the distant location to form small tumors known as micrometastases.
Angiogenesis: Micrometastases stimulate the growth of new blood vessels to obtain a blood supply. A blood supply is needed to obtain the oxygen and nutrients necessary for continued tumor growth.
Not all cancer cells can metastasize. In order to spread in this way, the cells must have the ability to penetrate the normal barriers of the body so that they can both enter and exit the blood or lymph vessels.
Spread through blood circulation:
If the cancer cells go into small blood vessels they can then get into the bloodstream. They are called circulating tumor cells. The circulating blood sweeps the cancer cells along until they get stuck somewhere. Usually they get stuck in a very small blood vessel called a capillary. Then the cell must move through the wall of the capillary and into the tissue of the organ close by. The cell can multiply to form a new tumor if the conditions are right for it to grow and it has the nutrients that it needs. Cancer cells in the circulation may try to stick to platelets to form clumps to give themselves some protection. Platelets are blood cells that help the blood to clot. This may also help the cancer cells to be filtered out in the next capillary network they come across so they can then move into the surrounding tissues.
Spread through lymphatic system:
The lymphatic system is a network of tubes and glands in the body that filters body fluid and fights infection. It also traps damaged or harmful cells such as cancer cells. If cancer cells go into the small lymph vessels close to the primary tumor they can be carried into nearby lymph glands. The cancer cells may get stuck there. In the lymph glands they may be destroyed but some may survive and grow to form tumors in one or more lymph nodes.
Picture: Figure 1&2: Show cancer cells trapped in the capillary and then the cell breaks through the capillary wall into the tissue.
Some people with metastatic tumors do not have symptoms. Their metastases are found by x-rays or other tests. When symptoms of metastatic cancer occur, the type and frequency of the symptoms will depend on the size and location of the metastasis. For example, cancer that spreads to the bone is likely to cause pain and can lead to bone fractures. Cancer that spreads to the brain can cause a variety of symptoms, including headaches, seizures, and unsteadiness. Shortness of breath may be a sign of lung metastasis. Abdominal swelling or jaundice (yellowing of the skin) can indicate that cancer has spread to the liver. Sometimes a person's original cancer is discovered only after a metastatic tumor causes symptoms.
Metastatic cancer may be treated with systemic therapy (chemotherapy, biological therapy, targeted therapy, hormonal therapy), local therapy (surgery, radiation therapy), or a combination of these treatments. The choice of treatment generally depends on the type of primary cancer; the size, location, and number of metastatic tumors; the patient's age and general health; and the types of treatment the patient has had in the past. In general, though, the primary goal of treatments for metastatic cancer is to control the growth of the cancer or to relieve symptoms caused by it.
The patient is a 38-year old woman who has recurrent breast carcinoma.
She was initially diagnosed with node-positive, left-sided breast cancer 8 years ago and underwent a mastectomy (removal of breast tissue) with adjuvant (to suppress secondary tumor formation) chemotherapy.
The patient appeared to be generally healthy but she reported that she had localized one pain, fatigue, and anxiety.
Her Karnofsky performance (a standard way of measuring the ability of cancer patients to perform ordinary tasks) was 80%.
A non-tender nodule is present at the incision cite where she had her mastectomy.
She had clear breath sounds, her heart sounded normal, and there was no edema or venous jugular pulsations.
The patient wished for visits every 3 weeks to receive monthly doses intravenously that consisted of docetaxel (100 mg/m^2) and trastuzumab (4 mg/kg) over 90 minutes.
At the first month follow-up, the patient appeared to be coping well, describing only moderate fatigue and anorexia.
Her Karnofsky performance status remained good.
Patient remained a normal weight.
Two weeks after the completion of her second cycle of chemotherapy, the patient appeared more debilitated
She began experiencing profound fatigue, and her Karnofsky performance dropped down to 40%
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