Silvio Berlusconi, the former Italian prime minister, is being treated in the intensive care unit of a Milan hospital for a lung infection related to a kind of leukemia that he has “had for some time,” his personal physician said on Thursday.

A medical bulletin issued by the physician, Dr. Alberto Zangrillo, said Mr. Berlusconi had chronic myelomonocytic leukemia, which was not acute, and that he was being treated both for the lung infection and for the blood cancer.

Mr. Berlusconi had been admitted to the San Raffaele hospital on Wednesday, for what Foreign Minister Antonio Tajani had described as “a problem related to a previous infection.”