In an ongoing registry study, incidence rates of all cancers combined were 15% higher than expected (Standardized Incidence Ratio [SIR]: 1.15, 95% CI 1.06 to 1.25), Samara Solan, MD, of the Icahn School of Medicine at Mount Sinai Medical Center in New York, and colleagues reported in Environmental Health Perspectives.
Incidence rates were also higher for thyroid, prostate, hematopoietic/lymphoid, and soft-tissue cancers, they found.
Solan acknowledged in a statement that the "findings of this study, while significant, should be interpreted with caution given the short follow-up and long latency period for most cancers; the intensive medical surveillance of this cohort by Mount Sinai researchers and our partners; and the small numbers of cancers at specific sites.
"However," she added, "our findings strongly highlight the need for continued follow-up and medical surveillance of WTC responders."
Solan and her colleagues analyzed data from their ongoing WTC Health Program, which has enrolled 20,984 workers who were involved in rescue efforts on and after Sept. 11. Overall, 575 cancers were diagnosed in 552 patients.
They found increases in incidence rates for several types of cancers that were higher than expectations:
All cancer sites combined SIR 1.15, 95% CI 1.06 to 1.25
Thyroid cancer: SIR 2.39, 95% CI 1.70 to 3.27
Prostate cancer: SIR 1.21, 95% CI 1.01 to 1.44
Combined hematopoietic and lymphoid cancers: SIR 1.36, 95% CI 1.07 to 1.71
Soft tissue cancers: SIR 2.26, 95% CI 1.13 to 4.05
They also saw positive associations for non-Hodgkin lymphoma and kidney cancer, but those weren't significant.
When the study was restricted to the 302 cancers diagnosed 6 or more months after enrollment, the incidence rates for all cancers combined and for hematopoietic/lymphoid cancers became nonsignificant, falling to SIR 1.06 (95% CI 0.94 to 1.18) and to SIR 0.77 (95% CI 0.49 to 1.16), respectively.
But thyroid and prostate cancer diagnoses still remained greater than expected, they wrote.
Lung cancer incidence rates were significantly lower than expected in both the initial and restricted analyses (SIR 0.89 and SIR 0.62, respectively), but it's not clear why this may be.
The researchers cautioned that the observation about thyroid cancer may be an artifact due to increased medical surveillance, particularly because there was no evidence of Iodine-131 -- which has a strong causal link to thyroid cancer -- at Ground Zero.
The case may be similar for prostate cancer, since patients may have been subject to more PSA screening as a result of more frequent medical care.
Solan and colleagues also found that the relative risk of all cancers combined was higher in those who had very high exposure to the rescue scene than in those with low exposure, but the finding was not significant (RR 1.40, 95% CI 0.70 to 2.76).
Risk was also higher for those directly exposed to the dust cloud (RR 1.13, 95% CI 0.79 to 1.61) and for those who experienced significant amounts of dust (RR 1.23, 95% CI 0.85 to 1.76), but again, those findings did not reach significance.
The findings are similar to those of other studies that have found a higher risk of cancer among World Trade Center rescue workers, but, the researchers noted, their findings differ from previous work because they are the first to look at varying levels of exposure.
The short follow-up time, they noted, is a major limitation of the study, since most occupational cancers become manifest at least a decade after the exposure. It was also limited because the WTC Health Program is a voluntary program, which raises the possibility of self-selection bias.
Still, they concluded that the findings highlight the need for prolonged follow up of these workers to assess their risks of cancer and other chronic diseases.
News Source: www.medpagetoday.com
