Senator John McCain has been diagnosed with glioblastoma, an aggressive form of brain cancer.The diagnosis comes less than a weekafter McCain, who is 80, had brain surgery on Friday to remove a blood clot above his left eye. Once the clot was taken out, doctors determined that itwas connected to brain cancer.The senator and his team of doctors at the Mayo Clinic in Arizona are reviewing treatment options, which could include radiation and chemotherapy.An aggressive brain cancerGlioblastoma is the most commonly diagnosed form of brain cancer, though it's still quite rare with only three cases per 100,000 people.The cancer tends to be treated with a combination of surgery to remove the tumor, radiation, and chemotherapy, according to the National Cancer Institute. The Mayo Clinic's statement about McCain's case did not mention surgery as one of the potential options for him (the procedure McCainhad was just to remove the blood clot), though it's unclear whether his doctors have ruled it out at this point.With the combination oftreatments, the median survival rate(ameasureof how long patients on the treatment tend to survive) is 14.6 months, according to the American Brain Tumor Association. The ABTA noted that the five-year survival rate for glioblastoma, or percent of people alive fiveyears after their diagnosis, was just 10%. Children with glioblastoma tend to farebetter than adults.McCain hasa history of melanoma, which is considered the most serious form of skin cancer. However, his glioblastoma is unrelated to that. The Mayo Clinic noted in a statement that this isa primary tumor, meaning that it's still in its original spot, rather than spreading around the body.Why brain tumors aretough to treatTreating brain cancer is a verydifferent processthan treating cancer in any other part of the body because of the blood-brain barrier, which stopscertain pathogensand molecules from passing from the blood into the brain.Theblood-brain barrieris key to keeping the brain safe, but because it's good at keeping things out, it's also hard to get drugs like chemotherapy in.There's also the challenge of tackling the mix of different cells that make up the tumor."The cells don't all behave the same way, so even when you kill some, the residual cells can take hold and grow again, so you're fighting a constant uphill battle to get rid of every last cell,"Susan Chang, director of neuro-oncology at University of California San Franciscotold Bloomberg.Advances in treatmentFormer Vice President Joe Biden tweeted out his support for his friend, McCain, on Wednesday. Biden's son Beau died in 2015 from brain cancer at 46. Biden subsequently launched a cancer moonshot initiativethat's brought him in contact with cancer doctors, researchers, and executives from around the world to discuss new treatment options for the disease.Incredible progress in cancer research and treatment in just the last year offers new promise and new hope. You can win this fight, John.' Joe Biden (@JoeBiden) July 20, 2017There have been a number of medical advances in the treatment of cancer in the past few years. One major advance has been immunotherapy.Unlikechemotherapy, which involves administering powerful drugs that kill both cancerous and healthy cells (most healthy cells can repair themselves), immunotherapies harness the power of the immune system to help it identify and knock out just the cancerous cells.One type of immunotherapy, called checkpoint inhibitors, have seen a fair amount of success in treating melanoma, lung cancer, bladder cancer, and blood cancers.Researchers are currently exploring whetherthese immunotherapiescould also fightglioblastoma, though there have been some setbacks and cases where survival hasn't improved.SEE ALSO:A cancer treatment that one expert called the 'most exciting thing I've seen in my lifetime' just got closer to approvalJoin the conversation about this storyNOW WATCH: 5 science-backed signs you might be smarter than average Click here to read full news..