On the brain
The highest percentage of all brain tumours that originate in the brain and central nervous system (CNS) are benign growths that occur in the meninges1, a structure consisting of three layers of protective tissue that surround the cerebral cortex. Most malignant primary brain tumours, however, occur in the cerebral cortex1 — with the highest percentage developing in the frontal lobe*.
26% Frontal lobe The frontal lobe constitutes almost two-fifths of the human brain. It has a role in modulating many brain functions, including voluntary movement, fluency of speech and expression of emotion. People with a tumour in this area often experience seizures as an initial symptom.
19% Temporal lobe Both hemispheres of the brain contain a temporal lobe. The lobe’s location, close to the ear, means that most of its functions are related to auditory processing. Surgical removal of tumours from the temporal lobe is challenging owing to the region’s complexity.
12% Parietal lobe The parietal lobe has differing roles in the left and right hemispheres of the brain. Tumours in the left lobe often affect a person’s speech, and those in the right lobe can affect perception of the physical location of body parts and understanding of geographical location.
5% Cerebellum Tumours in the cerebellum affect a person’s ability to coordinate voluntary movements such as balance and blinking.
4% Brain stem The brain stem connects the cerebral cortex to the spinal cord. Tumours in the region often affect a person’s ability to walk, speak and swallow, as well as their facial tension and vision.
3% Occipital lobe The occipital lobe is the smallest lobe of the cerebral cortex. It plays a part in processing visual information. Tumours in this lobe can cause loss of vision, visual disturbances and hallucinations.
2% Ventricle The ventricles are hollow parts of the brain that are filled with cerebrospinal fluid. Conventionally, intraventricular tumours are treated initially by draining excess cerebrospinal fluid using a shunt, which helps to relieve pressure in the brain.
30% Other regions Physicians strive to report the exact locations of brain tumours. However, such growths can sometimes extend into several areas of the brain, or their locations might not be recorded for various reasons.
*Percentages do not add up to 100% because of rounding.
The most common malignant primary brain tumour is a type of astrocytoma (a tumour that forms from glial cells) known as glioblastoma multiforme1. Glioma, a group of tumours that includes astrocytoma, comprises 27% of all tumours, and 80% of malignant tumours1.
Up to 30% of people with primary cancers in parts of the body other than the brain will develop brain metastases2. At least twice as many cases of secondary brain cancer as malignant primary brain cancer are diagnosed each year2.
Lung and bronchus Around 20% of lung cancers spread to the brain3 — the highest proportion of any cancer type.
Primary brain tumours are treated using a multipronged approach that can involve surgery, radiotherapy or chemotherapy. Yet the long-term outlook and survival rates of people with such malignancies remains poor.
The average years of life lost is a good measure of the extent to which life is cut short by various cancers. This is the sum difference in years between the ages at which people with a particular condition died and the ages to which they would otherwise have lived, divided by the total number who died.
Despite improvements in detection and treatment, the number of deaths from brain cancer has remained unchanged in the past three decades.
Against the clock
Brain tumours are classified using a grading system that ranks them from least (grade I) to most (grade IV) aggressive. Early diagnosis is linked to better survival times5.
Mind the gap
There are differences in the incidences of brain cancer in men and women, regardless of the age of those affected. Researchers are unsure why this might be.
About 55% of malignant brain tumours occurred in men, compared with 45% in women, between 2008 and 2012 in the United States1.
However, only around 36% of non-malignant brain tumours occurred in men, compared with 64% in women, during the same period in the United States1.
Nature 561, S40-S41 (2018)