There is a critical difference between primary brain cancer and secondary brain cancer. The former is cancer which develops in the brain tissue itself while the latter is cancer which begins developing in an organ or tissue elsewhere in the body and eventually metastasizes (spreads) to the brain.
PMBT is also known as the ‘primary malignant tumor of the brain and is a term frequently used in conjunction with brain tumors. It is a broad umbrella term for the various kinds of brain cancer which can originate from brain tissues as well as the central nervous system (CNS).
It is rare for a primary brain tumor to spread outside the CNS. But the reverse is not true. Tumors originating in other parts of the body can and in several instances do spread to the brain. In about 12.5% of all cancer cases, the disease will metastasize to the brain from the original site/organ. This is found to be true to a large extent in case of tumors originating in the breast, kidney, lung, and skin (malignant melanoma).
About 1% of the US population suffers from primary brain tumors. So assuming 1 for every 100,000, we can come up with an approximate annual number of 39,000 for those people who have been diagnosed with primary brain cancer. (Similarly estimated numbers for patients diagnosed with secondary or metastatic brain tumor would be about 170,000). From the earlier mentioned 39,000, a little under half will have malignant tumors and the rest benign. About 13,000 people in the US die annually of primary brain.
Over the past 20 – 25 years, an adjustment increase of 9% in terms of age has been incorporated in the death rate from brain cancer in both males and females. There has been a dramatic rise of the two below mentioned types of brain cancer in the adult population. Brain tumors primarily occur in two age groups: children (significantly between the ages 0 to 4) and then in an adult group (which levels off between 65 and 79 years). This report will deal with the second group. Brain tumors in adults are six times more common than in such tumors in children.
The general assumption of the brain is an organ which is made up of neurons (nerve cells). In addition to these neurons however, there are many other tissues within the spinal cord and of course the brain too. The function of these tissues is support, connect and protect the nerve tissues. There are at least 15 different cell/tissue types located in the brain and spine and a distinct tumor type can arise in any of these. Pathologists therefore identify 15 different types of CNS tumors.
Supporting cells tumors include the group known as astrocytomas. Within this group GBM or glioblastoma multiforme is the most common malignant form.
Neuron tumors include neuroblastomas, ganglioneuromas and neurocytomas.
There are also meningiomas which originate from the meninges. These are layers of protective lining that surround the brain and spinal cord (the infection meningitis affects this tissue). Other rare brain tumors include tumors which develop in the pituitary gland, pineal gland and the choroid plexus.
There are seven “families” within these tumors which make up the majority. GBM constitutes 40.6% of primary CNS tumors whereas astrocytomas make up 42.4%. These tumors account for 83% of all brain cancers in adults.
Roughly 15% is made up of Pilocytic astrocytomas, oligodendrogliomas, ependymomas, medulloblastomas, mixed oligoastrocytomas and meningiomas. Whatever else remains makes up 1.9 percent of the total number of CNS tumors.
The incidence of GBM and anaplastic astrocytoma seem to be increasing. Technology in the form of MRI machines and CT scans has played their part in this perceived increase. Early discovery of tumors means some patients have a shot at a longer survival which will have its own profound impact on health statistics. The CBTRUS or Central Brain Tumor Registry of the United States (www.cbtrus.org) is an organization which keeps accurate statistics on brain tumor cases.
By Chris Ryan and Dr. Mahesh Kanojia