When Izzie's cancer stopped growing, her case wasn't interesting enough to Dr. Rebecca Swender anymore. The case was handed over to Dr. Gendall, who scheduled further IL2 treatments for Izzie. He told Alex and Izzie that he didn't know how long it was going to take before Izzie would be completely cured, but that they should be happy with the fact that the aggressive cancer stopped growing.
Dr. Gendall is the only resident oncologist ever shown on either show.
Dr. Gendall is likely training to become a medical oncologist as he wears red scrubs. However, it's a possibility that he could still take a surgical oncology fellowship as oncology residents rounded under Dr. Swender.