Lou Alvarez ran into the rubble of the World Trade Center on 9/11, a moment he still remembers as so eerily quiet, it was like a movie set. NYPD Detective First Grade Alvarez, 51, now retired, would go on to watch his friends and colleagues fall ill, but he thought somehow he had dodged the bullet.

Fifteen years later, the day before Father’s Day 2016, the bombshell dropped, as he put it. Alvarez was diagnosed with Stage 4 colon cancer that had spread to his liver.

On Saturday, as his family laces up their sneakers to run in the ninth annual Damon Runyon 5K at Yankee Stadium, Alvarez is 20 chemo treatments in and is looking at his second surgery.

Alvarez said the most important thing about the run, which benefits cancer research, is keeping the “light on the first responders.”

“A lot of these cancers are taking 10 to 15 years to metastasize in the body. In the police department it’s still a big deal, but I think outside of the police department, people have forgotten,” he said. “And there are guys who are getting sick and they’re dying from a terrorist attack that happened [15] years ago...Lately I’ve just been seeing more and more.”

Alvarez first put on his NYPD uniform in October 1990 after six years with the United States Marine Corps. He spent two and a half years with the 108th Precinct in Long Island City, then 12 years with Queens narcotics until he joined the bomb squad in 2004. On July 4, 2010, Alvarez retired from the NYPD, took two weeks off and started a new career with the Department of Homeland Security. He trained TSA agents at Kennedy Airport to analyze suspicious baggage.

On Sept. 11, Alvarez was supposed to work from 10 a.m. to 6 p.m. That morning, his wife’s father said turn on the T.V. “and right away I just jumped in the car and went to work,” arriving right after the second tower fell.

“It was just something out of a movie,” he said. “Everything was rubble by then. There’s no noise, just smoke all around. Just everything covered in ash.”

They went in searching for people in wreckage. They didn’t find anyone.

In the weeks that followed, Alvarez worked in 12 hour shifts, searching the surrounding roofs for possible bodies and as part of the “bucket brigade,” loading up 5-gallon buckets with debris to sort through.

“You weren’t thinking, you were just reacting, just doing your job,” Alvarez said.

But the years went on and Alvarez’ three boys (now 14, 17 and 27 years old) grew up.

At a certain point, he started noticing the comments. He was looking thinner. He wasn’t trying to lose weight and had nosymptoms of illness, so he shrugged it off. When he finally went to the doctor for what he thought was a pulled muscle, and then kidney stones, the tests revealed something else.

“A lot of guys who were down there feel like they dodged a bullet, because that’s how I felt. Fifteen years later, nothing’s going to happen to me,” he said. “The bombshell drops and your whole life changes.”

Alvarez was told he had maybe two years to live. He was told to “get your affairs in order” and that the doctors would keep him “as comfortable as possible.” He was told the cancer in his liver was too advanced and surgery wasn’t an option.

But Alvarez wouldn’t back down. He’s been through 20 consecutive rounds of chemo, and just five weeks after his first surgery on May 17 he went back to work at the DHS. He’ll return to the hospital in September for a second surgery.

“The way I look at it is fighting this disease is a lot more mental,” he said. “I’m not giving into this without a fight ... I keep fighting until either I beat it or they find a cure.”

His oldest son, David Alvarez, who first ran in the Damon Runyon 5K at Yankee Stadium on 2015, was more than happy to get a team together for his dad. By July 12, Team Alvarez had raised more than $1,500, all of which would be donated to the Damon Runyon Cancer Research Foundation. After the race, the whole family will get together at the eldest Alvarez’s parent’s house in Astoria.

“Being able to get other people involved has been a big thing for me,” David Alvarez said. “When you’re dealing with something like this, you just feel helpless.”

Despite his preference for living a private life, Alvarez will take a selfie and post it on a private Facebook page for police officers. He hopes to encourage first responders to sign up for The World Trade Center Health Program, which he did after he was diagnosed. He’s also taken up woodburning — making plaques he donates to first responders, as well as other things.

Ultimately, Alvarez said he has a close-knit family and a great support system. His wife, Lainie Alvarez, said she was excited to do something to help raise money for cancer research.

“Just to get the awareness out there,” she said.