A long-term follow-up study of firefighters who responded to the 9/11 attack in New York City shows survivors had a two to three times greater prevalence of myeloma precursor disease (which can lead to myeloma, a type of blood cancer) compared with a control population, MedPage Today reports.

The study was conducted by researchers at Memorial Sloan Kettering Cancer Center in Manhattan, the New York City Fire Department, Albert Einstein College of Medicine and Montefiore Health System in the Bronx and was reported online in JAMA Oncology.

For the study, 781 white male firefighters who worked at the WTC site the day of the attack had their blood samples studied to assess the prevalence of monoclonal gammopathy of uncertain significance (MGUS), which occurs when the blood’s plasma cells produce an abnormal protein. The firefighters were between 50 and 79 years old. The cohort was then compared with MGUS in a nonexposed control group of men living in Minnesota.

The combined analysis showed that the prevalence of MGUS was 1.8 times higher in the New York firefighters. Light-chain MGUS, a subtype of the cancer precursor, occurred more than three times as often in 9/11 rescue workers than in a control group of individuals who reported no environmental exposure to the site.

Later, in a separate analysis, the researchers examined 16 cases of multiple myeloma  diagnosed between September 12, 2001, and July 1, 2017, among white male WTC firefighters. On average, their age at diagnosis was 57, while the national average age for a multiple myeloma diagnosis is 70.

“We carried out this new study to do more than just treat cancer,” said the study’s senior coauthor David Prezant, MD, a professor of medicine at Einstein, a pulmonary disease specialist at Montefiore and chief medical officer of the FDNY. “We wanted to find early, predictive signs of cancer that would allow us to screen people and monitor those found at risk. By detecting MGUS, which predicts the development of multiple myeloma, we are able to do that.”

Researchers pointed out the second part of this study proves correlation, not causation, between cancer risk and exposure to the site. However, they did note that rescue and recovery workers at the disaster site were likely exposed to large quantities of potentially carcinogenic substances while working. And although not everyone with MGUS will go on to develop myeloma, the researchers recommend that physicians screen first responders for both conditions.

Meanwhile, a second report in the same issue of JAMA Oncology projected that fire and rescue workers at the WTC site would develop significantly more cancers of any type, including melanoma, prostate cancer and thyroid cancer. Researchers estimate the cost of treating these cancers would be nearly $236 million over a 20-year period while claiming many lives.