Twenty-five years after the September 11, 2001 attacks, the World Trade Center Health Program continues to certify new cancers among people exposed to the disaster site and its aftermath. The number of cancer certifications remains substantial: more than 10,000 were recorded during the 12 months ending June 30, 2026. But the numbers alone do not answer some of the most difficult questions facing researchers and clinicians. What proportion of the cancers being diagnosed represents the long-term consequences of WTC exposure? How much of the observed increase reflects intensive medical surveillance? And why do cancer outcomes differ among racial and ethnic groups within the exposed population? The epidemiologic literature has provided important answers over the past 25 years. It has also left several questions unresolved.
Key Takeaways
- As of June 30, 2026, the WTC Health Program had recorded 57,044 cancer certifications among its members over the program’s life, including 10,393 cancer certifications during the preceding 12 months. A certification is not necessarily equivalent to a unique patient or a first cancer diagnosis. [1]
- Early FDNY research identified a modest excess of cancer among WTC-exposed firefighters, but the investigators cautioned that follow-up was still short and that surveillance bias and other confounding factors could not be excluded. [2]
- Thyroid cancer remains an important example of the difficulty in separating exposure-related risk from increased detection. Studies have found elevated thyroid cancer incidence in WTC-exposed populations, while other research has shown that medical surveillance substantially increases detection of asymptomatic disease. [3[[4][5]
- Cancer outcomes after diagnosis vary. Among WTC Health Registry enrollees with post-9/11 cancer, non-Hispanic Black patients had higher all-cause and non-cancer mortality than non-Hispanic White patients after adjustment for baseline and tumor characteristics. Socioeconomic status explained part, but not all, of the observed disparity. [6]
- Twenty-five years after the attacks, the central epidemiologic challenge is no longer simply documenting that cancers occur in the exposed population. It is determining which patterns can be attributed to specific exposures, how much detection has contributed to observed incidence, and how those findings should influence clinical care.
A Milestone Measured in New Certifications
The scale of the WTC Health Program provides an important measure of the continuing health burden. As of June 30, 2026, the program had 145,275 members and had recorded 57,044 cancer certifications over its lifetime. Of those certifications, 28,131 were among responders and 28,913 among survivors. [1]
Understanding the difference between a certification and a diagnosis is important. The program’s statistics count health-condition certifications, and individual members can have more than one certification. The June 2026 report therefore should not be interpreted as showing that 57,044 individual people have each developed a single WTC-related cancer. [1] During the 12 months ending June 30, 2026, the program recorded 10,393 cancer certifications. Cancer was the most frequently certified condition during that period. [1]
The program also applies minimum latency requirements before certifying a cancer. Current requirements include 2.5 years for thyroid cancer, 4 years for most other covered solid cancers, 11 years for mesothelioma, and 0.4 years for lymphoproliferative and hematopoietic cancers. [7] These requirements reflect the scientific literature the program uses to establish the minimum interval between exposure and diagnosis for coverage purposes. They do not, by themselves, establish that a particular cancer was caused by WTC exposure. Certification also requires that the member’s exposure meet program criteria and that a physician determine that the exposure was substantially likely to have been a significant factor in causing, contributing to, or aggravating the condition. [7][8]
This contrast matters as the population ages and cancer certifications continue to rise.
What the Firefighter Cohort Established—and What It Left Open
Some of the earliest and most closely followed cancer research came from the New York City Fire Department. In a 2011 study published in The Lancet, Zeig-Owens and colleagues examined 9,853 male firefighters employed as of January 1996. The cohort was particularly valuable because researchers had access to health information from before September 11 and experienced relatively little loss to follow-up. [2] Among WTC-exposed firefighters, the standardized incidence ratio for cancer compared with a demographically similar U.S. male population was 1.10 (95% CI, 0.98-1.25). When WTC-exposed firefighters were compared with non-exposed firefighters, the standardized incidence ratio was 1.19 (95% CI, 0.96-1.47) after correction for possible surveillance bias and 1.32 (95% CI, 1.07-1.62) without that correction. [2]
The investigators characterized the findings as a modest excess of cancer cases. They also urged caution.
The study covered only the first seven years following the attacks, a relatively short period for many solid tumors. The excess was not confined to a particular organ system, and the authors noted that they could not rule out unidentified confounding. They emphasized the need for continued follow-up. [2] Twenty-five years after the attacks, that caution remains relevant. The early FDNY analysis established an important signal, but it could not determine the contribution of individual components of the WTC exposure or fully separate exposure effects from differences in medical surveillance.
Thyroid Cancer: A Persistent Epidemiologic Question
Thyroid cancer illustrates the problem particularly well. Several studies have reported elevated thyroid cancer incidence among WTC-exposed populations. At the same time, research has demonstrated that medical surveillance can substantially increase the detection of otherwise asymptomatic thyroid cancers. [3-5] A 2021 review by van Gerwen and colleagues examined the evidence surrounding the reported excess of thyroid cancer in WTC-exposed populations. The authors noted that increased surveillance and physician referral could contribute to the observed incidence and emphasized that the extent of that contribution remained uncertain. They called for further investigation into a possible causal relationship between WTC dust exposure and thyroid cancer. [3]
The surveillance question is supported by more than theoretical reasoning.
In a study of 14,987 male FDNY rescue and recovery workers, 72 post-9/11 thyroid cancers were identified. Among the 65 cases for which the method of detection could be categorized, 53 were asymptomatic, and 12 were symptomatic. The age-standardized incidence of thyroid cancer was higher in the FDNY cohort than in comparison populations, but the excess was driven primarily by asymptomatic cancers. The rate of asymptomatic thyroid cancer was more than three times that observed in the Rochester Epidemiology Project comparison group. [4]
Another study compared WTC-exposed rescue and recovery workers enrolled in a medical monitoring program with WTC-exposed workers who were not enrolled and with the New York State population. Thyroid cancer incidence among participants in the medical monitoring program was more than twice the New York State rate, whereas incidence among non-participants was similar to the state population. The authors concluded that the findings supported an association between no-cost medical screening and increased identification of thyroid cancer. [5]
These studies do not prove that WTC exposure did not contribute to thyroid carcinogenesis. They demonstrate something more specific: surveillance can substantially affect the number and type of thyroid cancers detected in an exposed population. This is clinically important because thyroid cancer is particularly susceptible to overdiagnosis. A population subject to both a potentially relevant environmental exposure and intensive medical surveillance creates a difficult epidemiologic setting for determining how much of the observed increase reflects disease biology and how much reflects detection.
That answer remains unsettled.
A Population That Continues to Age
The WTC Health Program population is also changing. The current population includes first responders, recovery workers, survivors who lived or worked in the affected area, and others who meet the program’s eligibility criteria. The survivor population has become an increasingly important component of the program as people who were exposed while living, working, or attending school in Lower Manhattan continue to seek enrollment and medical monitoring. [1][8]
Recent data from Northwell Health provide a more localized view. Northwell’s WTC Health Program reported 177 certified cancer cases in 2023 and 235 in 2025, with another 132 cases recorded during the first half of 2026. The program reported 811 new cancer cases during the 42-month period beginning in 2023. Prostate and skin cancers were the most common, followed by breast and urinary tract cancers. [9]
The increase from 177 cases in 2023 to 235 in 2025 represents approximately a 33% increase over that interval.* These figures come from a single clinical center and should not be extrapolated to the entire WTC Health Program population. They do, however, illustrate an important feature of the current period: cancer diagnoses and certifications continue to occur among people exposed 25 years ago, including individuals who were not part of the original first-responder workforce.
Cancer Mortality and Racial and Ethnic Disparities
The epidemiologic questions extend beyond incidence. Kehm and colleagues examined 4,341 WTC Health Registry enrollees with a first primary invasive cancer diagnosed after September 11, 2001. Participants were followed through 2020. [6] Compared with non-Hispanic White enrollees, non-Hispanic Black enrollees had a higher risk of all-cause mortality after cancer diagnosis, with an adjusted hazard ratio of 1.20 (95% CI, 1.02-1.41). Their risk of non-cancer mortality was also higher, with an adjusted hazard ratio of 1.48 (95% CI, 1.09-2.01). [6] Hispanic enrollees had higher all-cause mortality and cancer-specific mortality in models that did not include socioeconomic status. Those associations were no longer statistically significant after including socioeconomic status in the full model. [6]
The investigators estimated that socioeconomic status accounted for 24% of the excess all-cause mortality risk among Black enrollees and 29% among Hispanic enrollees compared with White enrollees. [6] That leaves a substantial proportion of the disparity unexplained by the variables available to the researchers. This finding matters because exposure to the same disaster does not eliminate the broader social and structural factors that influence cancer outcomes. Access to care, socioeconomic circumstances, comorbidities, treatment, stage at diagnosis, and other factors can continue to shape survival after a cancer diagnosis. The study did not identify a single explanation for the observed disparities. Its conclusion was narrower: racial and ethnic disparities in mortality were present among WTC Health Registry enrollees with post-9/11 cancer, and additional research is needed to identify the factors responsible. [6]
The Post-9/11 Military Population Is a Different Epidemiologic Question
The health effects observed among WTC-exposed populations should not automatically be combined with those observed among veterans deployed to Afghanistan and Iraq after September 11. Exposure histories differ, as do the populations, study designs, and potential confounders. Gaffey and colleagues examined breast cancer incidence among 576,601 women veterans receiving Veterans Affairs primary care between 2001 and 2021. Approximately 24.6% had deployed in support of Operation Enduring Freedom or Operation Iraqi Freedom. [10]
Contrary to an expectation that deployment might be associated with increased breast cancer incidence, deployed women were 23% less likely to be diagnosed with breast cancer than non-deployed women in the study population (95% CI, 0.73-0.86). The association persisted after adjustment for healthcare utilization and across age and race strata. [10]
The authors proposed two possible explanations: a healthy-soldier effect, in which healthier individuals are more likely to be selected for and retained during deployment, and differences in breast cancer screening between deployed and non-deployed veterans. They did not interpret the finding as evidence that deployment exposures protect against breast cancer. [10] The study is relevant to the broader discussion because it demonstrates the difficulty of interpreting cancer incidence in populations defined by a major event or exposure. Selection into the population, healthcare utilization, surveillance, and other factors can influence observed cancer rates independently of a direct carcinogenic effect.
Revisiting an Early Risk Estimate
The evolution of the evidence can also be seen by revisiting one of the earliest quantitative assessments of cancer risk following the attacks. In 2005, Nolan and colleagues modeled the lifetime risk of asbestos-related cancer among Lower Manhattan residents attributable to asbestos released during the collapse of the World Trade Center. They used both an asbestos fiber-type-specific model and the U.S. Environmental Protection Agency model, which did not distinguish fiber types and combined mesothelioma and lung cancer risk. [11]
The fiber-specific model produced an upper-limit estimate of fewer than one excess asbestos-related cancer case over the exposed population’s lifetime. The EPA model produced an upper-limit estimate of 12 cases. The authors concluded that the asbestos-related cancer risk to Lower Manhattan residents from the collapse was negligible. [11] That conclusion needs to be read within the scope of the study because it addressed modeled asbestos exposure among Lower Manhattan residents. It did not estimate the cancer risk associated with the complete mixture of contaminants encountered by firefighters, rescue workers, recovery workers, or others at the site. Nor could a model developed in 2005 incorporate decades of subsequent epidemiologic follow-up.
Later assessments of the WTC environment have documented a complex mixture of particulate matter, metals, asbestos, synthetic vitreous fibers, volatile organic compounds, polycyclic aromatic hydrocarbons, dioxins, and other contaminants. [12] The early asbestos model and subsequent epidemiologic studies therefore answer different questions. The former estimated risk from one component of the exposure under specific assumptions. The latter examine observed health outcomes in populations exposed to a much more complex environmental mixture.
What the Evidence Means for Clinical Practice
For clinicians, the immediate issue is less about resolving every epidemiologic uncertainty than recognizing the population in front of them. Patients with a history of exposure to the World Trade Center disaster who are not enrolled in the WTC Health Program may be eligible for medical monitoring and treatment of certified conditions. The program covers cancer when the applicable exposure, latency, and certification requirements are met. [7][8]
The current program rules are explicit: a cancer must be included among covered conditions, the exposure must meet program requirements, the minimum latency period must be satisfied, and a program physician must determine that the 9/11 exposure was substantially likely to have been a significant factor in causing, contributing to, or aggravating the condition. [7,8] For oncologists and primary care physicians, a patient’s exposure history is therefore clinically relevant.
However, it is also important not to overstate what that history means. A cancer diagnosis in a person who was present at the World Trade Center site is not, by itself, proof that WTC exposure caused the cancer. Conversely, uncertainty about causation should not be interpreted as evidence that the exposure was irrelevant. The distinction between clinical certification, epidemiologic association, and individual causation should remain clear.
For thyroid cancer in particular, the literature supports a careful discussion of detection and overdiagnosis. The evidence shows that intensive surveillance identifies additional asymptomatic thyroid cancers in WTC-exposed populations. It does not establish that all of the excess incidence is attributable to surveillance, nor does it exclude a contribution from WTC exposure. [3][4][5]
What Still Remains Unknown
Twenty-five years of follow-up have established that cancer is an important component of the long-term health burden among people enrolled in the WTC Health Program. They have also established that the epidemiology is complicated. Cancer certifications continue to accumulate, but certification counts do not reflect unique patients or incident cancers. [1]
Cancer incidence has been elevated in some WTC-exposed cohorts, but early studies could not completely separate exposure effects from surveillance and other sources of bias. [2] Thyroid cancer remains a particularly important test case because increased surveillance clearly affects detection, while a possible contribution from WTC exposure remains an open research question. [3][4][5]
And cancer survival is not uniform across the population. Racial and ethnic disparities persist among WTC Health Registry enrollees with cancer, with socioeconomic status explaining only part of the observed differences. [6] The next phase of research will therefore need to do more than count cancers. It will need to refine exposure assessment, distinguish surveillance effects from disease incidence, examine specific tumor types and molecular characteristics, and identify the factors that contribute to differences in outcomes after diagnosis.
These findings will, no doubt, inform clinical decision-making. Twenty-five years after the attacks, physicians are still caring for patients whose cancers may have developed after years of latency, while researchers are still trying to determine precisely what the exposure did, to whom, and under what circumstances.
The epidemiologic record has become substantially stronger since 2001.
And… it is not yet complete.
Note
* Northwell’s September 2026 announcement described the change as a 75% increase, but the reported case counts do not produce that percentage. [9] For that reason, this article uses the underlying case numbers rather than the reported percentage.
References
[1] Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. World Trade Center Health Program External Quarterly Program Summary. Program data through June 30, 2026. Published August 1, 2026.
[2] Zeig-Owens R, Webber MP, Hall CB, Schwartz T, Jaber N, Weakley J, Rohan TE, Cohen HW, Derman O, Aldrich TK, Kelly K, Prezant DJ. Early assessment of cancer outcomes in New York City firefighters after the 9/11 attacks: an observational cohort study. Lancet. 2011 Sep 3;378(9794):898-905. doi: 10.1016/S0140-6736(11)60989-6. PMID: 21890054; PMCID: PMC5525140.
[3] van Gerwen M, Cerutti JM, Rapp J, Genden E, Riggins GJ, Taioli E. Post-9/11 excess risk of thyroid cancer: Surveillance or exposure? Am J Ind Med. 2021 Oct;64(10):881-884. doi: 10.1002/ajim.23268. Epub 2021 Jun 22. PMID: 34157150.
[4] Colbeth HL, Genere N, Hall CB, Jaber N, Brito JP, El Kawkgi OM, Goldfarb DG, Webber MP, Schwartz TM, Prezant DJ, Zeig-Owens R. Evaluation of Medical Surveillance and Incidence of Post-September 11, 2001, Thyroid Cancer in World Trade Center-Exposed Firefighters and Emergency Medical Service Workers. JAMA Intern Med. 2020 Jun 1;180(6):888-895. doi: 10.1001/jamainternmed.2020.0950. PMID: 32310290; PMCID: PMC7171583.
[5] Goldfarb DG, Colbeth HL, Skerker M, Webber MP, Prezant DJ, Dasaro CR, Todd AC, Kristjansson D, Li J, Brackbill RM, Farfel MR, Cone JE, Yung J, Kahn AR, Qiao B, Schymura MJ, Boffetta P, Hall CB, Zeig-Owens R. Impact of healthcare services on thyroid cancer incidence among World Trade Center-exposed rescue and recovery workers. Am J Ind Med. 2021 Oct;64(10):861-872. doi: 10.1002/ajim.23277. Epub 2021 Jul 18. PMID: 34275137; PMCID: PMC8796202.
[6] Kehm RD, Li J, Cone JE. Racial and ethnic disparities in mortality among World Trade Center Health Registry enrollees with post-9/11 cancer. Cancer Med. 2024 Aug;13(16):e70071. doi: 10.1002/cam4.70071. PMID: 39190574; PMCID: PMC11348902.
[7] Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. World Trade Center Health Program Member Handbook: Cancer Latency and Certification Requirements. Updated 2026. Online. Last accessed on September 10, 2026.
[8] Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. World Trade Center Health Program Frequently Asked Questions: Cancer in the WTC Health Program. Updated 2026. Online. Last accessed on September 10, 2026.
[9] Northwell Health. Cancer Cases Explode Among WTC Health Patients, Underscores Ongoing Crisis 25 Years After 9/11. Press release. September 8, 2026. Online. Last accessed on September 10, 2026.
[10] Gaffey AE, Han L, Ramsey CM, Skanderson M, Dziura J, Driscoll M, Burg MM, Brandt CA, Bastian LA, Haskell SG. Post-9/11 deployment history and the incidence of breast cancer among women veterans. Ann Epidemiol. 2023 Jan;77:98-102. doi: 10.1016/j.annepidem.2022.11.010. Epub 2022 Dec 5. PMID: 36470323.
[11] Nolan RP, Ross M, Nord GL, Axten CW, Osleeb JP, Domnin SG, Price B, Wilson R. Risk assessment for asbestos-related cancer from the 9/11 attack on the World Trade Center. J Occup Environ Med. 2005 Aug;47(8):817-25. doi: 10.1097/01.jom.0000167273.17109.6d. PMID: 16093931.
[12] Lioy PJ, Weisel CP, Millette JR, Eisenreich S, Vallero D, Offenberg J, Buckley B, Turpin B, Zhong M, Cohen MD, Prophete C, Yang I, Stiles R, Chee G, Johnson W, Porcja R, Alimokhtari S, Hale RC, Weschler C, Chen LC. Characterization of the dust/smoke aerosol that settled east of the World Trade Center (WTC) in lower Manhattan after the collapse of the WTC 11 September 2001. Environ Health Perspect. 2002 Jul;110(7):703-14. doi: 10.1289/ehp.02110703. PMID: 12117648; PMCID: PMC1240917.
[13] Landrigan PJ, Lioy PJ, Thurston G, Berkowitz G, Chen LC, Chillrud SN, Gavett SH, Georgopoulos PG, Geyh AS, Levin S, Perera F, Rappaport SM, Small C; NIEHS World Trade Center Working Group. Health and environmental consequences of the World Trade Center disaster. Environ Health Perspect. 2004 May;112(6):731-9. doi: 10.1289/ehp.6702. PMID: 15121517; PMCID: PMC1241968.
Disclosure
The relationship between WTC dust exposure and thyroid cancer incidence, and the extent to which surveillance bias versus a true carcinogenic effect explains the reported excess, remains an open scientific question as characterized by van Gerwen et al.; this editorial does not resolve that question and takes no position beyond what the cited literature states. This article is intended for informational purposes for healthcare professionals and does not constitute medical advice.
Featured image: © 2025 – 2026 – Stefan Szankowski/911 Museum, Greenwich Street, New York, NY, USA. Used with permission under the Unsplash License. In memoriam – The mangled remains of FDNY Ladder Company 3’s fire truck stand as a haunting artifact within the National September 11 Memorial & Museum, its twisted metal frame and scorched red panels bearing witness to the devastation of that day. This vehicle, whose crew responded to the World Trade Center and never returned, is preserved exactly as recovered. Museum visitors quietly observe the wreckage, reflecting on the sacrifice it represents. This powerful exhibit honors the bravery of first responders lost on September 11, 2001.
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