Original story comes from The National Enquirer, so...
'He put off the doctors for weeks after he first started experiencing the symptoms because he was afraid of what they would find,' the source said.
'Now the prison docs are telling him they believe he has a brain tumor. They plan to run a series of tests on him, MRIs and CT scans.'
The Enquirer reports that Simpson has finally agreed to the tests and is convinced he hasn't got long to live, telling a friend, 'I feel the end coming. But I don't want to die in prison like common jailhouse scum.'
The publication reports he has even begged President Obama for a pardon so he can die comfortably at home.