BRAIN TUMORS

A brain tumor is a mass of abnormal cells that is growing in or around the brain. It develops when abnormal cells multiply for unknown reasons. Benign and malignant are used to describe brain tumors. Benign brain tumors are usually slow growing with distinct borders, and have a normal appearance under a microscope. Malignant tumors are called brain cancer. They tend to be invasive into healthy areas of the brain and may grow rapidly. A benign tumor may be considered malignant if its size or location in a critical area of the brain may be life-threatening.

Primary brain tumors start within the brain. Secondary or metastatic brain tumors come from cells which have broken away from cancers within the body and traveled to the brain. Metastatic brain tumors are always considered malignant since they evolve from cancerous cell and grow rapidly.

What Causes a Brain Tumor?

Brain tumors are usually caused by a change in genetic structure. This change in genetic structure may be inherited, caused by the environment, or both. Only a low percentage (5%) of primary brain tumors are associated with inherited genes alone. However, a study by Bondy et al. (1994) showed that 80% of patients with glioblastoma multiforme had more than one copy of chromosome seven.

Mutated or missing genes result in abnormal cells. If abnormal cells have malignant potential, they will form a tumor when they multiply.

High-dose ionizing radiation, used to treat brain tumors, may on rare occasions be associated with the production of secondary brain tumors. This most often occurs from radiation treatments that are given over time. People exposed to certain chemicals, such as petrochemicals, pesticides and formaldehyde, appear to be at higher risk of developing a malignant brain tumor than those who are not exposed. In laboratory experiments, some viruses caused brain tumors in animals. It is unknown whether viruses can cause brain tumors in humans. Electromagnetic fields have been under study for some time as there appears to be a connection to brain tumors.

There are many environmental and genetic factors that can cause brain tumors. However, in most cases, we just don't know what causes a brain tumor.

Tumor Grading

Tumors are graded based on their microscopic appearances. The grade indicates the level of malignancy. Tumors are graded on their mitotic index (growth rate), vascularity (blood supply), presence of a necrotic center, invasive potential (border distinctness) and similarity to normal cells.

Malignant tumors may contain several grades of cells. The most malignant grade of cell found determines the grade for the entire tumor, even if most of the tumor is a lower grade.

In the World Health Organization grading system, grade I tumors are the least malignant. These tumors grow slowly and microscopically appear almost normal; surgery alone may be effective. However, even a grade I tumor may be life-threatening if it is inaccessible for surgery. Grade I tumors are often associated with long-term survival.

Grade II tumors grow slightly faster than grade I tumors and have a slightly abnormal microscopic appearance. These tumors may invade surrounding normal tissue, and may recur as a grade II or higher tumor.

Grade III tumors are malignant. These tumors contain actively reproducing abnormal cells and invade surrounding normal tissue. Grade III tumors frequently recur, often as grade IV tumors.

Grade IV tumors are the most malignant and invade wide areas of surrounding normal tissue. These tumors reproduce rapidly, appear very unusual microscopically and are necrotic (have dead cells) in the center. Grade IV tumors cause new blood vessels to form, to help maintain their rapid growth.

Types of Treatment

Various treatments may be used to treat a malignant brain tumor. The type and number of treatments given is dependent upon many factors, including the size of the tumor, its growth rate and the symptoms the patient is experiencing. Patients should realize that there is more than one way to treat their tumors and should seek medical treatments where many options and a continuum of treatments are available.

Biopsies

Surgical biopsies of brain tumors are no longer considered absolutely necessary because of the development of new imaging techniques. With the current scanning ability with contrast dyes, CT and MRI scans, a brain tumor may be diagnosed as malignant or benign without opening the skull for a biopsy. There has always been controversy over whether the act of obtaining a biopsy may allow the spreads of cancerous cells to other brain areas.

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