Metastasis of lung cancer to the brain,one of the most common cases of spread of lung cancer
Lung cancer is known to spread to the brain in about 40 percent of cases in which a metastasis has occurred. Metastasis is the medical term used to describe a cancer which has spread beyond the initial tumor to a different, distant organ system. With lung cancer, this is considered stage 4 of the disease.
Prognosis of Lung cancers with metastases to the brain is changing for people. Unlike many chemotherapy drugs, some of the newer targeted therapies for lung cancer are able to penetrate the blood-brain barrier and can help fight lung tumors which have spread to the brain. There are also new options available for those who have only a few metastases to the brain (sometimes defined as oligometastases).
When metastases happen in people with lung cancer, the secondary malignancy is not considered a "brain cancer" but rather "lung cancer metastatic to the brain" or "lung cancer with brain metastases." In contrast, the term brain cancer is used for those tumors which originate in the brain as the primary, rather than secondary, malignancy.
In other words, if you were to take a sample of the cancer cells in the brain they would be cancerous lung cells, not cancerous brain cells.
The cause of lung cancer metastasis to the brain
Lung Cancer cells, visible under a microscope and detectable by a technique called flow cytometry, separate from the primary tumor and enter the circulatory (blood) system. The immune system attempts to destroy these migrating blood-borne cancer cells. However, if the number of cancer cells becomes very high, the immune system may become overwhelmed or tolerant of these cells. Scientists believe circulating tumor cells use the bloodstream or lymph system for access to other organs, initially migrate and enter the lungs, then move on to other organs and in particular, the brain.
Some scientists believe cancer cells may break away from the primary cancer site while that cancer is still in its earliest stages. Research shows that these traveling cells (circulating tumor cells) exit the blood or lymphatics and enter another part of the body. In a new organ, the tumor may lie dormant or rapidly enlarge causing new symptoms referable to the new site of metastasis. The growth of metastatic tumors is often independent of the primary site of cancer from which the tumors originated.
In some situations, the process of tumor spread and growth in the metastatic organ occurs rapidly. Since blood from the lungs flows directly to the brain, lung cancer is capable of quickly spreading to the brain. Sometimes, this happens so fast that the brain metastases are found before the primary lung cancer is found.
Symptoms of Spreading Lung Cancer to the Brain
Brain metastases can occur with either small cell lung cancer or non-small cell lung cancer.
Small cell lung cancer is often difficult to diagnose in the early stages and, as a result, may spread to the brain before a diagnosis is even made. Non-small cell cancers can also spread to the brain but tend to do so later in the course of the disease after the primary tumor has been discovered.
Symptoms can vary based on the type of lung cancer and where in the brain the metastases occur.
Frustratingly, as many as a third of all people with secondary brain cancer will have no symptoms whatsoever. If they do occur, they typically include:
- Loss of balance
- Nausea and vomiting
- Difficulty walking
- Loss of coordination
- Speech problems
- Vision changes, including loss of vision or double vision
- Peripheral weakness (occurring on one side of the body)
- Memory loss
- Personality changes
If your doctor suspects that your lung cancer has spread to your brain, he or she will order imaging tests such as computed tomography (CT scan) which use X-rays to create diagnostic images or a magnetic resonance imaging (MRI) which does the same with magnetic waves. While an MRI is considered more accurate, it may not be used in persons with certain metal implants (including non-safe pacemakers).
Another type of imaging tool is positron emission tomography (PET scan) which is able to differentiate between normal cell metabolism and those which appear hyperactive (such as cancer cells). If a suspicious lesion is found but the diagnosis is uncertain, a biopsy may be performed to obtain a tissue sample for evaluation.
The treatment of brain metastases depends on a number of factors including how much of the brain is involved and your overall health.
If brain metastases are widespread, treatment is focused on controlling the symptoms and complications in order to optimize quality of life. If there are only a few metastases, local treatment to eliminate the metastases entirely is often pursued.
Steroids such as Decadron (dexamethasone) may be used to control any swelling of the brain, while anticonvulsive medications (seizure drugs) can reduce the incidence and severity of seizures. Other treatments can be broken down into general treatments for stage 4 lung cancer, treatments for widespread brain metastases, and localized treatments for oligometastases.
General treatments for cancer wherever it is present may include:
Many chemotherapy drugs are ineffective in treating brain metastases due to the presence of the blood-brain barrier, a tight network of capillaries which serves to keep toxins (including chemotherapy drugs) out of the brain. Chemotherapy may, however, reduce the size of tumors in the lungs and therefore limit their ability to spread to the brain.
Targeted drugs for EGFR mutations, ALK rearrangements, ROS1 rearrangements and more are sometimes able to penetrate the blood-brain barrier. Some of the newer drugs appear to be more effective in doing so. Like chemotherapy, these drugs also control the primary tumor and thus limit its ability to spread to the brain.
It's still too soon to know much (the first immunotherapy drug for lung cancer was approved in 2015) but the three immunotherapy medications approved for lung cancer show promise in their ability to reduce brain metastases. For some people, these drugs have led to both control of metastases and a "durable response" to the cancer as a whole.
Treatments which specifically address brain metastases but designed to treat widespread metastases:
If there are several brain metastases present (cancer centers vary in defining this and the number may be greater than three to greater than 20), whole-brain radiotherapy has traditionally been recommended. Whole-brain radiation may be a good choice for those who have symptoms related to their brain metastases or who are at risk for complications (such as a stroke(لینک به سکته مغزی)). It can also be used after surgery to reduce further spread of the cancer. While not designed to cure cancer, at least 50 percent of people undergoing whole-brain radiotherapy will notice some improvement in symptoms. Common side effects can include memory loss (especially verbal memory), skin rash, and fatigue. Radiation oncologists often recommend a medication which appears to reduce cognitive dysfunction related to this treatment.
Metastasis-specific treatment options include:
Also known as stereotactic radiosurgery or SBRT, this is a type of high-dose radiation given to a specific area of the brain. Since the radiation is targeted, side effects are typically less severe and offer better survival rates than whole-brain therapy. This form of radiotherapy is usually reserved for people with three or fewer tumors, although some people have had this treatment for up to 20 tumors.
Proton therapy is used in a way similar to SBRT, and is done in an attempt to eradicate the metastases which are present.
Surgery is used less commonly but may be an option if there are one or a couple of tumors that are easily accessed, and there are no signs of cancer elsewhere. Surgery may involve the complete removal of a tumor or the partial removal to alleviate symptoms. Whole-brain radiation typically follows. Since small-cell tumors are more responsive to radiotherapy alone, surgery is more often used to remove non-small cell cancers.
If the various treatment options prove ineffective, palliative care may be used to offer relief and reduce stress associated with a terminal diagnosis. This may include the use of pain medications, physical and occupational therapy, or complementary treatments to enhance comfort and improve the quality of life.