What Is Glioblastoma and Why Is It So Deadly?

By Steve Blanchard - July 22, 2021

Over the past few years, it seems more and more celebrities have announced a glioblastoma diagnosis. In 2018, Sen. John McCain passed away following a bout with the illness, and in early 2020 Rush drummer Neil Peart suffered a similar fate.

But what exactly is glioblastoma and why is it so deadly?

“Glioblastoma is the most aggressive type of brain cancer and considered to be advanced by the time of diagnosis,” said Dr. Solmaz Sahebjam, a neuro-oncologist at Moffitt Cancer Center. “Currently it is not curable, meaning there’s no way to eradicate all cancer cells. The aim is to control the tumor for the longest possible time and try to preserve a patient’s quality of life, as it is going to be significantly affected by the tumor over time.”

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"Currently it is not curable, meaning there’s no way to eradicate all cancer cells."

- Neuro-Oncologist

Unlike other brain tumors that start in the body and spread to the brain, glioblastoma starts in the brain or spinal cord. Primary brain tumors are relatively rare, with fewer than 25,000 Americans diagnosed with them each year. Metastasized tumors, however, are more prevalent and an estimated 400,000 are diagnosed in the United States each year.

“In a glioblastoma you have two parts to the disease,” said Dr. Michael Vogelbaum, chief of Neurosurgery and program leader of Neuro-Oncology at Moffitt. “There is the solid part and there is the infiltrating part that co-exists with normal, functioning brain tissue. There is no safe way to remove all of that infiltrating part of the disease while keeping the brain function intact.”

That said, removal of the solid part is most often feasible and when done completely can help patients survive longer. There are few glioblastomas that are completely inoperable.

Diagnosing glioblastoma, requires surgery and a biopsy. If a tumor is cancerous, treatment can vary based on the patient. Those diagnosed with glioblastoma typically live 10 to 22 months.

Ongoing research may slowly unlock new treatments for glioblastoma, including immunotherapy. A small trial reported by the University of California at Los Angeles in early 2019 found that patients with recurrent glioblastoma who were given the checkpoint inhibitor Keytruda® prior to surgery lived, on average, 417 days. That’s longer than the average survival rate of 228 days.

The treatment is a form of immunotherapy, and the study marks the first time an immune system treatment has shown any benefit to glioblastoma patients. Authors of the study were quick to add that glioblastoma was not cured in the trial participants and that the early phase study involved fewer than three dozen patients.

While the study is small and can make it difficult to draw broad conclusions, Vogelbaum says it does have merit.   

“The study is remarkable in two ways,” he said. “First, it is one of the few studies that carefully evaluated the effects of treatment on brain tumor tissues. Secondly, it used the surgical procedure itself to help prime the immune system to attack any residual tumor left after surgery.”

Glioblastoma suppresses the immune system, not only at the site of the cancer but throughout the body. That makes it difficult to find effective treatments, especially since tumors like this differ in their characteristics and behavior. Keytruda blocks a protein known as PD-1, which prevents T cells from seeing and attacking the cancer. By disabling that protein, the immune system can better attack a tumor.

There has also been some progress in the field of genetics, which may help scientists detect DNA signatures that could predispose some people to this type of cancer. Right now, the only way to know if you’re at risk of a glioblastoma is to know the signs, including drastic changes in headaches or cognitive functions. 

Chronic, unexplained headaches are especially common, as are neurological complications such as seizures and double vision. Not every headache means cancer. But if a headache is out of the “normal” parameters for a patient, or other symptoms such as personality or mood changes present themselves, it may be time to see a doctor.

Other glioblastoma symptoms include:

  • Vomiting
  • Changes in temperament or personality
  • Difficulty speaking or responding to other peoples’ speech
  • Difficulty swallowing
  • Short-term memory loss
  • Fainting
  • Loss of appetite
  • Muscle weakness in the arms or legs 

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