Rob Serra was just 21 and had not even started in his new job as a New York City firefighter when terrorists brought down the World Trade Center’s twin towers on Sept. 11, 2001.

“I just got out of the academy on Sept. 10,” Serra told NBC News last week. He spotted the burning skyscrapers from the Verrazano-Narrows Bridge, called his firefighter brother for guidance and hopped on a bus to get as close as possible.

“I had no idea what I was doing. I had never been to a fire before,” Serra said.

He joined the crowds of first responders pawing through the chunks of building material, breathing in the pulverized dust loaded with cement, asbestos, lead, glass fibers, dioxins and other chemicals.

“Everyone had a half inch of white paste on their face,” Serra recalls.

Now, 17 years later, he and thousands of others are still paying for the time they spent in Lower Manhattan.

“I do remember thinking that this is probably going to kill me,” Serra said.

“You figure two buildings full of glass, asbestos, steel. You could taste it,” he added. “I hope I have a lot of years left, but common sense and reason tells me I don’t.”

His sinuses are full of scar tissue from the removal of growths called polyps and he says he has some evidence of neurological damage, including trouble walking. Serra fears that he will develop cancer.

“We all think it’s coming at some point,” he said. “It’s just a matter of when, not really if.”

Three hundred forty-three firefighters and paramedics were among the 2,753 people who died in the fires and in the collapse of the two buildings on Sept. 11, 2001. More than 150 have died since, according to Dr. David Prezant, chief medical officer of the New York Fire Department.

Several programs are trying to keep track of the health problems plaguing people directly affected by the 9/11 attack in New York and its aftermath. There’s a federally funded program for people with documented illnesses, including dozens of different cancers, asthma and other respiratory problems, post-traumatic stress disorder, and long-term problems caused by injuries.

The World Trade Center Health Program, established by the 2010 James Zadroga 9/11 Health and Compensation Act — named for a New York City police officer whose death was linked to his work at ground zero — helps people with illnesses that have documented links to the disaster.

Dr. Michael Crane, who directs the program at the Icahn School of Medicine at Mount Sinai Hospital in New York, says 72,000 people are enrolled, including firefighters and police officers but also utility workers, medical examiners and others. Of them, he says, 8,000 already have cancer.

He expects many more cases.

“Some of the toxic exposures … the effects of those are now due,” he said.

Asbestos-related cancers, notably lung cancer, can take 20 years for symptoms to show. “It’s time for them to start appearing,” Crane told NBC News.

“I am concerned about rising cancer rates.”

Many of the cancers are treatable, including the most common skin cancers related to the chemical exposures. For that reason, not too many cancer deaths can be directly blamed on 9/11.

But other cancers will be deadly. Earlier this year, a team at Memorial Sloan Kettering Cancer Center in New York reported that 9/11 firefighters had an elevated risk of multiple myeloma, among other cancers.

The researchers said all of those exposed to the toxic dust at ground zero need continued careful surveillance.

Because of the health issues, many of those who helped with cleanup and recovery can no longer work.

Elizabeth Wilson, a former city bus driver who was assigned to work with other transit workers at ground zero after the attack, is one of them. Now 59, she retired two years ago. She has nodules, a potentially precancerous type of growth, in her lungs; asthma; acid reflux; and other conditions that have been certified as having been caused by the 9/11 dust.

Like so many people living and working at ground zero, Wilson never wore a face mask. “It was like a cloud,” Wilson said. “You couldn’t see your hand in front of you, it was so bad.”

Only about half of those assigned to work in the area wore protective gear, and even fewer of the people living and working nearby did.

“We were supposed to have been fitted for respirators at the time,” Wilson told NBC News. But Christine Todd Whitman, then the Environmental Protection Agency administrator, erroneously assured people that the air was safe to breathe. “I never got a mask after that,” Wilson said.

Whitman has since said she regrets having said that.

Wilson said her clothes were covered in so much dust during the first days and weeks that she would stuff them into yard waste bags and throw them out rather than trying to wash them.

Many more people were similarly exposed, and don’t even know that they are at risk or that help is available, said Dr. Gaetane Michaud, a lung health specialist at New York University.

"I feel heartbroken to know that if at the lowest number, we're saying there are about 400,000 people that should be benefiting from the World Trade resources, and about 80,000 are actually benefiting from them,” Michaud said in a statement.

"It's not just lung cancers. It's lung cancers, breast cancers, esophageal cancers and thyroid cancers, to name a few. These people should be screened and be taken care of.”