The Gary Sinise Foundation shared the news on Instagram of Sinise’s death on Tuesday, with the caption, “In Honor & Memory of McCanna ‘Mac’ Sinise 1990-2024.” In a statement, the foundation said that on August 8, 2018, Mac was diagnosed with a very rare cancer called chordoma. The foundation said chordoma is cancer that originates in the spine and only affects an average of 300 people in the U.S. per year.

In a lengthy tribute to Mac that Sinise 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. As parents, it is so difficult losing a child,” Sinise wrote.

Actor Gary Sinise's Son Dies After Battling A Horrendous Form Of Cancer

He continued, “My heart goes out to all who have suffered a similar loss, and to anyone who has lost a loved one. We’ve all experienced it in some way. Over the years I have met so many families of our fallen heroes. It’s heartbreaking, and it’s just damn hard.”

“Our family’s cancer fight lasted for 5 ½ years, and it became more and more challenging as time went on,” Sinise added. “While our hearts ache at missing him, we are comforted in knowing that Mac is no longer struggling, and inspired and moved by how he managed it.”

“He fought an uphill battle against a cancer that has no cure, but he never quit trying. Mac loved movies, and we always told him he reminded us of the soldier at the end of the extraordinary film ‘1917,’ running through the battlefield, bombs going off all around him, knocking him down one after the other, yet he keeps getting back up, refusing to quit and keeps running forward.”

“I am so blessed, fortunate, and proud to be his dad,” Sinise shared.

In his post, Sinise explained that the summer of 2018 was a “particularly challenging time” for his family. The “Forrest Gump” star said his wife, Moira, was diagnosed with stage 3 breast cancer in June of that year. She underwent surgery to remove lymph nodes and began chemotherapy and radiation treatment.

Two months later, Mac was diagnosed with chordoma. Sinise said he was bewildered at the time since he had never heard of the very rare cancer.

“And two cancer patients, mother and son, within two months of each other? A real punch in the gut,” he wrote. “I went online to see what I could find. Chordoma is a one in a million cancer. Originating in the spine, Chordoma affects, on average, only 300 people in the U.S. per year. In 70% of the cases the initial tumor can be removed, and it is cured. But in 30% of the cases, perhaps about 90 people per year, the cancer returns.”

Moira went into remission after receiving treatment for months and has since remained cancer-free. In September 2018, Mac underwent surgery to remove the initial tumor, but his cancer returned by May 2019 and was spreading.

“This began a long battle that disabled him more and more as time went on,” Sinise wrote.

Mac went on to have four additional spinal surgeries and continued to receive chemotherapy and radiation treatment. Sinise wrote that eventually the cancer caused Mac to become paralyzed from the chest down, though he “still had limited use of his right arm, and fingers on his left hand.”

Sinise recalled that in 2020, Mac stepped down from his position as the assistant manager of education and outreach at the Gary Sinise Foundation to focus on his rehabilitation and recovery as he prepared for his fifth spinal surgery.