The St. Paul Pioneer Press said Flynn announced in February 2011 he had stage III metastatic prostate cancer.
"It's heartbreaking," WCCO, Minneapolis, news anchor and longtime friend of Flynn Frank Vascellaro told the Minneapolis Star Tribune.
Vascellaro said many people are unaware of "what a huge, worldwide success he was an author, because when you met him, he was just Vinny from St. Paul, a guy from a big Irish family who was grounded in his values and convictions, a loyal friend and an extraordinarily generous person who helped all kinds of people both publicly and privately."
Flynn's books have sold more than 15 million copies in the United States and millions more worldwide, said his publisher, Simon & Schuster.
Flynn's 14th book, "The Survivor," is due out in November.