Gary Sinise’s son has died at the young age of 33. The Forrest Gump actor’s only boy, McCanna Anthony Sinise, whom the family lovingly calls Mac, passed away early last month after a five-year battle with a rare cancer called Chordoma, RadarOnline.com has learned. Gary shared the heartbreaking news on his foundation’s website Tuesday, revealing Mac had “one in a million cancer” that only affects an average of 300 people in the U.S. every year. Mac died on January 5 at 3:25 PM and was laid to rest on January 23. Gary revealed his son was diagnosed with Chordoma in 2018, just months after his wi…