Director Stephen Gyllenhaal may have found his next project -- and it's a topic very close to him.
Gyllenhaal -- father to Oscar nominees Jake and Maggie and 10-year-old Luke -- was with his youngest son at a swimming pool last year when an unusual feeling washed over him.
"My arms and legs suddenly felt as thick as elephants, and I could hardly move," Gyllenhaal, 75, recalled to The Post. "I was really freaked out, but I kept on thinking it's nothing, and then it got worse and worse."
After three days of being unable to pee, Gyllenhaal was diagnosed with prostate cancer that had spread to a nearby lymph node.
For years, he had taken a wait-and-see attitude to his enlarged prostate and elevated prostate-specific antigen (PSA), two potential signs of the deadly cancer.
With September being Prostate Cancer Awareness Month, Gyllenhaal is publicly sharing his diagnosis for the first time while advocating for a proactive approach to testing and disease management.
"Just stay on top of it because almost all the time, you're relieved," Gyllenhaal said about testing.
"You say, 'I've got another two years before I have to do anything again,' and it really matters to do that," he added. "[If] something comes up two years later, you've caught it early, and you deal with it, and you don't die."
Prostate cancer is the most common cancer among US men, aside from skin cancer.
Nearly 314,000 new cases of prostate cancer and over 35,000 deaths will be recorded this year, making it the second leading cause of cancer death in men, behind lung cancer, according to new American Cancer Society estimates.
Gyllenhaal's road to cancer goes back a ways. His doctor flagged him about his enlarged prostate many years ago and his elevated PSA in 2020.
PSA is a protein produced by healthy and cancerous prostate cells. A high PSA blood test result can signal prostate cancer, but it is not a definitive diagnosis.
Gyllenhaal -- who directed 2023's "UnCharitable" documentary -- said he got distracted by the pandemic, and it “didn’t quite register” that his condition could be serious even as he received a Gleason score of 5 in 2022.
The Gleason grading system ranges from 2 to 10, with a higher score indicating a more aggressive cancer.
"That's what got me to suddenly do everything quickly," Gyllenhaal said, noting his inability to urinate stemmed from a bladder infection. "My prostate was out of control."
After consulting with friends and doctors, he ended up connecting with Dr. Arpit Chhabra, a radiation oncologist and director of education at the New York Proton Center in East Harlem.
There are a few ways to address prostate cancer, including removing the entire prostate gland, using high-energy radiation to kill cancer cells or freezing the cells away with focal therapy.
Proton therapy uses a beam of charged particles to deliver a targeted, high dose of radiation to a tumor, sparing healthy tissue.
Conventional radiation therapy has historically been less precise.
"Proton therapy allowed us to deliver this curative treatment with the greatest precision and safety, minimizing side effects to surrounding organs," Chhabra told The Post.
Gyllenhaal, a Hollywood Hills resident, temporarily relocated to Maggie's place in Brooklyn for the nearly eight weeks of treatment. He found joy in the sunrise in his daily commute to the facility.
There were no notable side effects from radiation, though he has experienced downsides to taking the hormone medications Orgovyx -- which reduces testosterone production -- and Nubeqa, which blocks testosterone from fueling cancer cells.
"There's no question about it, that's been the hardest thing," Gyllenhaal said about his lower testosterone which has led him to lose weight and muscle mass. He also struggles with his short-term memory.
Nevertheless, he's optimistic about his prognosis.
"I don't understand the proton stuff," Gyllenhaal shared, "but it has definitely made my life kind of feel miraculous" and has me hopeful about the future.
There's no history of prostate cancer in his famous family, but his diagnosis means Jake, 44, and Luke are at increased risk.
Gyllenhaal said Jake is "so on top of this."
"It was funny; he was worried that I wasn't on top of it," Gyllenhaal said.
"He had this top doctor; his top doctor said: 'Your dad's got all the right people.' " he continued. "'He's doing the best thing he can do,' which was really good."
He said he's also had frank talks with young Luke and these discussions will continue as he gets older.
Men at higher risk of prostate cancer should generally start testing between 40 and 45, while those at average risk should look to begin testing from 45 to 50.
Screening every two to four years is recommended for men 50 to 69 years old.
Though Gyllenhaal rang the bell at the Proton Center, denoting the end of his treatment, he won't say he's cancer-free. He notes that he's still doing hormone therapy as well as taking medicine for his heart.
He has contemplated starting a book project about his wellness journey -- and his stance may surprise some.
"This sounds glib," Gyllenhaal said, "but it's kind of the best thing that's ever happened to me." stressing that many things have stressed him out over the years but cancer trumps them all.
"It kind of means you have to wake up and face life and not live in a fantasy," he added. "I live in Hollywood so 'fantasy' is my middle name and it takes the stress out."