The cancer that cost Mayor Bob O'Connor his life was far more aggressive than anyone had expected, said his attending physician, Dr. Stanley Marks, director of clinical services at UPMC Hillman Cancer Center.

The central nervous system lymphoma did not respond to any of the treatments that were tried, he said. An MRI scan performed two days before Mr. O'Connor's death on Friday revealed that cancer had spread through his spinal cord.

Also, the mayor had headaches for perhaps several months before he went to doctors seeking help, Dr. Marks said. However, the doctor added, considering the aggressiveness of the cancer, earlier diagnosis and treatment might not have saved his life.

Read a complete report of Anita Srikameswaran's interview with Dr. Marks in tomorrow's Pittsburgh Post-Gazette.