The 86-year-old entertainer known as the “Pianist to the Presidents” because of his many presidential performances writes in an email message to friends that he started chemotherapy last week.

He says doctors told him the tumor cannot be removed because of its size. When chemotherapy shrinks the tumor to an operable size, Williams says surgeons will remove it.

Williams says he’s not canceling any upcoming concerts. He performed Sunday at Del Webb’s Sun City retirement resort in Palm Desert, and his personal assistant says the concert was sensational.