The NYPD lost 23 members on September 11, but more than 100 more officers have died from 9/11-related illnesses since then, and more are fighting for their lives. NY1's Clodagh McGowan has one sergeant's story.
Friends and colleagues of NYPD Sergeant Chris Christodoulou have not forgotten him. They visit him at his Long Island home, sharing stories and some laughs.
"They're a terrible group of guys and girls," the sergeant said with a smile.
Christodoulou's life has changed dramatically in the past 16 years; he had three children, and the family moved from his native Brooklyn to the suburbs.
But last year, there was a change no one expected. "Unfortunately, I have brain cancer," Christodoulou said.
He has Stage 4 Glioblastoma, a relatively rare and aggressive cancer. In Christodoulou's case, it is believed to have been caused by exposure to toxins at the World Trade Center site.
"I was assigned to an election post in Coney Island, and that's when the first plane came over the radio," Christodoulou recalled. "I ran to the station house and volunteered to jump in a van.
"We got there before the first tower fell."
His dad Bill is a retired firefighter who has lost friends and colleagues to the attack and to subsequent sickness.
"I hate to say it's a unique club; it's something that's kind of a club you don't want to join," Bill Christodoulou said. "You'd rather be healthy, be able to raise your children."
Chris's wife says the hardest part is watching her husband, a devoted hockey coach to their sons, forced to the sidelines at the age of 46.
"To see him so active with his family and the kids, and now he's fighting so hard, and he fights every day for them," Melissa Christodoulou said.
The tumor is inoperable, so Christodoulou is relying on immunotherapy to shrink it. For his brothers and sisters in blue, his fight has become an all too common reality.
"More guys died from 9/11-related illnesses than died that day," NYPD Officer Billy Montemarano said.
As Christodoulou reflects on the 16th anniversary of 9/11, he can't help but think of his colleagues.
"Hopefully nobody else gets sick," he said.
Christodoulou's colleagues say they are, of course, thinking of him.
"We're Team Chris all the way. We're always here for him," a friend said.