Gary Sinise's son 'Mac' dies following cancer battle

FILE - Gary Sinise visits SiriusXM Studios on February 11, 2019 in New York City. (Santiago Felipe/Getty Images)

Gary Sinise's son, McCanna "Mac" Sinise has died from a rare form of cancer. He was 33 years old. 

The Gary Sinise Foundation confirmed the news of his passing on Instagram Tuesday, with the caption, "In Honor & Memory of McCanna ‘Mac’ Sinise 1990-2024."

In a lengthy tribute to Mac that Gary shared on his website, the 68-year-old actor revealed that his son died on Jan. 5, 2024, at 3:25 p.m. and was laid to rest on Jan. 23.

"Like any family experiencing such a loss, we are heartbroken and have been managing as best we can," his dad said in a statement. "As parents, it is so difficult losing a child. My heart goes out to all who have suffered a similar loss, and to anyone who has lost a loved one." 

He continued, "I am so blessed, fortunate, and proud to be his dad."

According to the foundation, Mac was diagnosed with a very rare cancer called Chordoma, in August 2018. 

McCanna "Mac" Sinise diagnosed with rare cancer called Chordoma

The foundation said that Chordoma is cancer that originates in the spine and only affects an average of 300 people in the U.S. per year.

Gary, known for movies such as "Forest Gump," wrote that Mac's diagnosis came just months after his wife Moira Harris received a stage three breast cancer diagnosis. While Moira went into remission and has remained cancer-free following treatment, Gary wrote that Mac's disease spread over time. 

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A graduate of USC Thorton School of Music, Mac had a passion for drumming, composition and songwriting. However, his disability rendered him unable to continue playing the drums or piano.

Gary said that he only spoke publicly for the first time about Mac's illness in a December 2023 interview with Fox News, in which he mentioned his health challenges, but focused on highlighting the music Mac was working on in the final months of his life.

"Mac was living out a dream, bringing it to reality with his collaborating partner, Oliver,"  he wrote. "It was incredibly motivating and therapeutic for him, and he was so excited to see it all come together."

In lieu of gifts or flowers, people can contribute to the Chordoma Foundation or the Gary Sinise Foundation.

Mac is survived by his father, mother and two sisters.

FOX News contributed to this story.