Dr. Hahn specializes in lung cancer and sarcoma. He has moved up the ranks at M.D. Anderson since arriving in 2015, when he served as chairman of the radiation oncology department. In 2017, he was named the hospital’s chief operating officer and in 2018, the chief medical executive. Before coming to M.D. Anderson, he was chairman of the radiation oncology department at the University of Pennsylvania’s Perelman School of Medicine from 2005 to 2014.
Dr. Hahn has donated to Republicans in the past, though not to the Trump campaign. In 2017, he gave $1,000 to the New Pioneers PAC, a group affiliated with Representative Greg Walden, Republican of Oregon, who was then chairman of the House Energy and Commerce Committee, which oversees the F.D.A. In earlier election cycles, he donated to candidates from both parties, including $706 to Mitt Romney, the Republican presidential nominee, in 2012 and $250 to the congressional campaign of Rep. John Murtha, a Democrat, in 2008.
Dr. Sharpless, by contrast, had donated to Democrats, including $500 to the presidential campaign of Barack Obama in 2012 and $250 in 2008.
Dr. Hahn is seen as a skilled leader, with a laid-back, friendly approach that has helped to speed his ascendancy at the institutions where he has worked. More recently, he was a finalist for chief medical officer at the Memorial Sloan Kettering Cancer Center, but the job was ultimately given to the person who had been serving in the acting role.
In 2017, Dr. Hahn stepped in to run M.D. Anderson after Dr. DePinho announced his resignation. At the time, the cancer center was operating at a financial loss, and a series of scandals involving Dr. DePinho — including his ties to for-profit companies — had taken a toll on morale, as did the layoffs of about 800 people.
“Steve was asked to right the ship, and he did,” said Dr. Otis Brawley, the former chief medical and scientific officer at the American Cancer Society, who is now a professor of oncology and epidemiology at Johns Hopkins University.
By the end of the year, M.D. Anderson had returned to financial stability.
“He has the ability to stand up, take responsibility, understand the problem and fix the problem so it won’t happen again, and help everybody through that,” said Dr. Theodore DeWeese, the vice dean for clinical affairs at Johns Hopkins University School of Medicine.