Journalist Jeff Todd, who helped Porter write "The Man Behind the Bow Tie," says Porter's family announced Monday his illness has worsened and he needs alternative treatment in hospital.
Porter has been detained since May 2013 in a Panamanian prison as he fights extradition to Canada. He faces fraud charges in Canada related to a $1.3-billion hospital project in Montreal.
The doctor says he has cancer and has been treating himself while imprisoned in Panama.
Todd said in an email that members of Porter's family are travelling to Panama to be with him.
Porter's wife, Pamela Porter, was sentenced in December to 33 months in jail after she pleaded guilty to two counts of money laundering in connection with her husband's case.