He shared the news in a written statement posted to his personal Instagram. The message was shared as a collaborative post with the official Chicago Cubs Instagram account.
"To my Chicago Cubs, National Baseball Hall of Fame, extended Baseball Family, the city of Chicago, and all my loyal fans, I want to share some personal news," Sandberg said. "Last week, I learned that I have been diagnosed with metastatic prostate cancer. I have begun treatment, and I am surrounded by my loving wife Margaret, our incredibly supportive family, the best medical care team, and our dear friends. We will continue to be positive, strong, and fight to beat this. Please keep us in your thoughts and prayers during this difficult time for me and my family."
Stay in the game with the latest updates on your beloved Chicago sports teams! Sign up here for our All Access Daily newsletter.
The Cubs also released a statement of their own.
"Ryne, we're sending love, strength and support your way," the team said. "With locked arms, we are rallying around you and your family on the journey ahead to conquer this battle."
Sandberg is a legendary figure in Cubs history, having been acquired by the club from the Philadelphia Phillies in January 1982. He won the 1984 National League MVP Award, and during his career he was a 10-time All-Star, a seven-time Silver Slugger winner and a nine-time Gold Glove winner.
In 16 big-league seasons, Sandberg hit 282 home runs and drove in 1,061 RBI’s, and was elected to the Baseball Hall of Fame in 2005. His No. 23 jersey has been retired by the Cubs, and he was immortalized with a statue outside the ballpark.
Sandberg was also drafted by the Phillies and played one season for them in 1981.
He was the third base coach and infield instructor for the Phillies after the 2012 season and was then promoted to interim manager in 2013.
He was then named the permanent manager of the Phillies later that year before resigning in 2015.