Robert N. Taub, a doctor and government witness in the federal corruption case against the State Assembly speaker, Sheldon Silver, is leaving his position as the head of a Columbia University cancer center, and the center is being disbanded, a university spokesman said Friday.

Dr. Taub, 78, a prominent researcher and clinician in the arcane field of abdominal mesothelioma, a type of cancer linked to asbestos exposure, began the Columbia University Mesothelioma Center more than a decade ago.

He is a major player in the criminal complaint against Mr. Silver, who was arrested on Thursday.

“The research and patient care activities of the mesothelioma center are being absorbed into the division of hematology/oncology,” Douglas Levy, a Columbia University Medical Center spokesman, said on Friday.

Mr. Levy said Dr. Taub would no longer serve as director, but it was unclear whether he would continue serving patients at Columbia. He remains a professor at the university.