Glioblastoma is one of the deadliest cancers. Experts tell Healthline it is extremely aggressive and difficult to treat.

Senator John McCain’s diagnosis of glioblastoma, a type of brain cancer, means he joins the estimated 12,000 Americans diagnosed with this cancer every year.

On Thursday, the senator’s office released a statement announcing McCain’s diagnosis after undergoing a procedure to remove a blood clot above his left eye.

“Subsequent tissue pathology revealed that a primary brain tumor known as a glioblastoma was associated with the blood clot,” the senator’s office said in the statement.

While the cancer is rare, it is deadly and difficult to treat.

With McCain’s diagnosis, new attention is being paid to the disease and the experimental treatments being used.

Glioblastoma is a type of brain cancer that develops from the star-shaped glial cells.

This type of cancer is the most common form of brain cancer and is extremely aggressive.

“It’s one of the most lethal, if not the most lethal cancers,” Dr. John Boockvar, director of the Brain Tumor Center at Lenox Hill Hospital in New York City, told Healthline.

The estimated survival rate is approximately 15 months, according to the American Association of Neurological Surgeons (AANS).

Boockvar said for a patient in their 80s the expected median survival rate may be as low as eight months, but cautioned that each patient is different.

This type of brain cancer is far different from the one that affected former President Jimmy Carter.

Carter’s cancer was a metastasis of melanoma, while McCain’s cancer is separate from his previous melanoma tumors.

Additionally, new immunotherapy treatments have been found effective at targeting the type of cancer Carter had, while there is nothing significantly effective to treat McCain’s cancer.

This type of cancer affects only two to three adults out of 100,000 every year, according to the AANS.

Men are more likely to be affected, and the disease is most likely to develop in people aged 45 to 70.

People of Caucasian or Asian descent are also more at risk, according to the MD Anderson Cancer Center.

The American Brain Tumor Association estimates that in 2017 there will be 12,390 new cases diagnosed.

Symptoms of the disease include headache, vomiting, and seizures. This type of cancer can also cause memory loss and subtle personality changes.

Depending on where the tumor is in the brain, it can also affect a person’s vision or speech.

Despite decades of research, there’s been little success in prolonging patients’ survival, according to Boockvar.

“The treatments have only improved survival by one month per decade of research we’ve done,” said Boockvar. In 50 years, “we’ve improved survival about five months.”

In general, doctors will recommend surgery followed by chemotherapy and radiation. McCain’s office confirmed he and his family are considering this line of treatment.

“The senator and his family are reviewing further treatment options with his Mayo Clinic care team,” his office said in a statement. “The senator’s doctors say he is recovering from his surgery ‘amazingly well’ and his underlying health is excellent.”

Treating the cancer is difficult in part because of its location.

The brain is protected from foreign agents that can get into the blood or lungs via a membrane called the blood-brain barrier.

“It’s bad if you have a disease of the brain, you can’t get drugs into the brain,” said Boockvar. “We have a host of clinical trials in an attempt to overcome the blood-brain barrier.”

However, he said getting through the blood brain barrier can be dangerous because it can require some amount of “leaky” vessels to get the medication through.

If it leaks too much, it can damage the brain.

While the cancer remains challenging to treat, there are a few new options for patients that could be reason for hope.

One unusual treatment involves wearing an electric cap to kill tumor cells. In 2015, the FDA approved the Optune device, which uses electrodes to target the tumor.

The patients have to shave their heads and wear the cap, which has alternating electrical fields called “tumor treatment fields.” These fields target new cells within the brain, hoping to kill or at least stall the tumor’s growth.

The cap does not cure the cancer and is supposed to be used in conjunction with recommended chemotherapy treatment.

The FDA found that those who used the cap in conjunction with recommended chemotherapy lived an average of 19 months after starting treatment compared with 16 months for people who received only chemotherapy.

Boockvar said he also always tries to get patients into some sort of clinical trial if they have a glioblastoma diagnosis.

In recent years, more and more patients have been put into immunotherapy trials, where the immune system is harnessed to try and kill or diminish the cancer.

Carter was treated with a new immunotherapy drug called Keytruda, which blocks certain protein actions, thereby allowing the immune system to go after the cancer growths.

But that drug will only work in cancers that have a specific genetic marker more common in melanoma and lung cancer.

For glioblastoma new treatments include vaccines that target a specific kind of peptide only expressed on glioblastoma cells, re-engineering a patient’s T cells to target likely cancer cells, and changing T cells so they don’t “stand down” when faced with tumor cells, but attack them as foreign bodies.

None of these treatments have been proven to be effective at stopping the cancer, but experts are hopeful one or more could seriously prolong patients’ lives.

“Just the fact that we have some phase III trials in glioblastoma, where for years we had a hard time getting past phase II trials, is an encouraging sign,” Dr. Michael Lim, who directs the brain tumor immunotherapy program at the Johns Hopkins Kimmel Comprehensive Cancer Center, said in a statement on the National Cancer Center website. “So, for the first time in a long time, there’s some real excitement.”