Cancers of the nervous system that affect adults
Kathryn E. Vinson, MS, CCRC
As with cancers that affect the liver, cancers that hit the brain and nervous system can be broadly broken down into primary tumors and secondary tumors. A primary brain or nervous system tumor is one that arises from tissues in the brain and nervous system (think back to some of those definitions I gave you earlier such as glial cells or astrocytes), while secondary tumors are those that have traveled from another place (think breast cancer that has metastasized to the brain). And, as with cancer in the liver, secondary tumors of the brain are more common in adults than are primary brain tumors. Today we are going to be talking about primary brain tumors in adults. So, grab a copy of those definitions if you need, and let’s get sciency.
Staging and Grading
When we talk about brain tumors, we often refer to grade rather than stage. This may seem weird at first, but there is a perfectly logical reason. In most cancers, staging talks about how far the cancer has spread, to what structures it has spread, and the size of the primary tumor; however, here is a biggie – brain tumors rarely metastasize to other parts of the body. Here we go again with this ever-present question – why? Our body has some amazing features that are designed to protect itself. One of these is called the blood-brain barrier. This barrier keeps most big nasty bugs (bacteria and viruses) from getting into the brain, and it also keeps great big cells – such as tumor cells – inside and prevents them from spreading.
Now you’re thinking, “Hang on a second. These tumors stay put for the most part, so why are they so dangerous?” The simple answer is that the tumors can affect the processes of the body that are controlled by the region of the brain where they grow. Tumor growth can also increase intracranial pressure, which leads to a whole host of symptoms on its own.
Given this, we talk about grading with brain tumors, using Roman numbers I-IV. Grade I tumors are the least aggressive and least likely to invade nearby brain tissue, while grade IV tumors grow quickly and need the most aggressive treatments. This grading system applies to both adult and pediatric cancers.
Causes of Brain Tumors in Adults
Sadly, not a whole lot is known about the causes of brain and nervous system tumors in adults. There are some inherited conditions (such as Li-Fraumeni and von Hippel-Lindau syndrome) that seem to predispose people to these cancers by affecting certain tumor suppressor genes. While we know that cancers arise when gene changes happen within a cell allowing it to grow out of control, scientists don’t have a firm grasp on why these changes happen in the brain, as the brain is protected from the majority of toxicities such as nicotine by the blood-brain barrier.
Types of Brain Tumors in Adults
- Gliomas – this is a somewhat generic term that refers to tumors that arise from the glial cells. These account for about 30% of primary brain tumors in adults. Gliomas can be further broken down into astrocytomas, ependymomas, and oligodendrogliomas. This category also makes up the majority of fast-growing tumors. These types of cancers can be very difficult to remove completely with surgery alone, given that they arise from supporting structures in the brain, and have a tendency to travel along pathways for cerebrospinal fluid (CSF).
- Astrocytomas, one of the sub-types of gliomas, account for about 20% of adult brain tumors. They range from grade I non-infiltrating astrocytomas, to the very aggressive grade IV glioblastoma. Glioblastomas are the most common malignant brain tumor in adults.
- Oligodendrogliomas are rare, accounting for only 2% of brain tumors. Most are grade II, but anaplastic oligodendrogliomas are considered grade III.
- Ependymomas – these types of tumors only account for 2% of tumors. This type of glioma originates in the cells that line the ventricles of the brain and travel along CSF pathways. These guys can block the places in the brain where the CSF leaves the ventricles, which can cause increased intracranial pressure and also a condition known as hydrocephalus. If there is a fortunately in cancer, unlike other gliomas, ependymomas don’t typically grow into normal brain tissue, and can be often be successfully removed with surgery.
- Meningiomas – these tumors can arise in both the brain and spinal cord from the tissues that surround those structures. With 1 out of 3 tumors of the brain and nervous system being a meningioma, this represents the largest class of the diseases. Of these, 80% are grade I and can usually be removed easily with surgery, if they are not too near vital areas of the brain or cord. Grade II and III meningiomas are more aggressive and can grow into bone and move to other parts of the body. These tumors are twice as more common in women than in men, and are most often diagnosed in the 40s and 50s.
- Schwannomas – this rare (only about 8% of CNS tumors) form of tumor comes from the Schwann Cells – which insulate the ends of nerves and is responsible for creating the myelin sheath. Given this, these tumors can occur in both the central nervous system and peripheral nervous system.
There are a few other types of brain and spinal cord tumors that occur in adults, but are more prevalent in children, so we will discuss those in my next post covering pediatric brain and nervous system tumors.
As always, much love, many prayers, and abundant blessings to all of the warriors out there!