John McCain's Cancer: What is glioblastoma?

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In July 2017, Sen. John McCain was diagnosed with glioblastoma, an aggressive brain tumor.

The senator underwent surgery to remove a blood clot in late July 2017 at the Mayo Clinic in Phoenix, Arizona. Lab results from the surgery confirmed the presence of glioblastoma.

What is Glioblastoma?

Unlike other brain tumors that start in the body and spread to the brain, glioblastoma starts in the brain or spinal cord. The tumor arises from star-shaped brain cells known as"astrocytes." The American Brain Tumor Association (ABTA) labels the tumor "highly malignant" and cancerous because of its ability to invade and stay within normal brain tissue.

Glioblastoma is the most common of all malignant brain tumors, representing 15.4% of all primary brain tumors, according to the ABTA.

This form of tumor killed Sen. Ted Kennedy and Beau Biden, the son of former vice president Joe Biden.

What are the symptoms of Glioblastoma?

The symptoms of glioblastoma are usually a result of increased pressure on the brain. The ABTA lists headaches, nausea, vomiting and drowsiness as symptoms of the tumor. Depending on where the tumor is, however, weakness on one side of the body, memory and speech difficulties and visual changes can all be developed as a result.

What is the treatment for Glioblastoma?

There is no specific treatment used for glioblastoma, instead there are a few different approaches doctors can take,  said CNN's Chief Medical Correspondent Dr. Sanjay Gupta.

When a cancer is malignant, this means cells are dividing uncontrollably and can invade nearby tissues. They may also spread to other parts of the body through the bloodstream or lymph system in the body.

What is the prognosis for Glioblastoma patients?

The ABTA labels the prognosis for glioblastoma survival in terms of median survival -- the length of time at which an equal number of patients do better and an equal number of patients do worse. Depending on the type of glioblastoma and treatment used, this can range from 14 months to three years.

The association also cites a 2009 study that found 10% of patients with glioblastoma may live five years or longer. The average survival time for malignant glioblastoma is around 14 months with treatment, Gupta said.

CNN's Susan Scutti contributed to this report.

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