U.S. Senator John McCain is being treated for glioblastoma multiforme, one of the most aggressive forms of brain cancer.
It is a malignant tumor that grows at a very rapid rate and is able to shift to new locations within the brain, according to the Mayo Clinic, a non-profit medical research group.
Glioblastomas generate microscopic roots that penetrate brain tissue, making complete surgical removal impossible, Mayo says.
McCain's doctors at the Mayo Clinic Hospital in southwestern city of Phoenix, Arizona said they removed all of the tumor that was visible on brain scans and that the senator's treatment options may include a mix of radiation and chemotherapy.
Mayo Clinic says the average survival rate for glioblastoma patients who receive aggressive treatment combining surgery, radiation and chemotherapy is about 14 months, with only 27-percent surviving two years.
For patients who respond favorably to initial treatment, the cancer can return frequently within one to two years. The American Cancer Society estimates the survival rate for patients older than 55 at about four percent.
The tumors, which are rare, usually develop in adults. The American Brain Tumor Association expects nearly 12,400 new cases this year.
Scientists are attempting new treatments for glioblastomas, including one that leverages the patient's immune system to invade the cancer. The treatment has been used for blood cancers, but its effectiveness on solid brain and other tumors is unknown at this time.
A device that creates electric fields to attack cancer has improved the survival chances of glioblastoma patients.