After recent tests it was revealed tonight that Williams was diagnosed with the illness.
He will continue in his role as senior development coach at Richmond throughout his treatment.
Port Adelaide chief executive Keith Thomas said Williams will be in the thoughts of the entire Port Adelaide community.
"The Williams family name is synonymous with Port Adelaide and 'Choco' is loved and revered by so many of our supporters, past players, volunteers, staff and administrators," Mr Thomas said.
"Only a few weeks ago he returned to the club to celebrate the tenth anniversary of our first AFL premiership and as always he stole the show.
"On behalf of the entire Port Adelaide community we wish him well in his treatment."
