Daylight at Last for Study of Diesel Lung Cancer Risks

After 20 years of research and almost as many years fighting industry groups in court for control of their data, government scientists can finally publish two papers showing that underground miners exposed to diesel fumes have a threefold increased risk for contracting lung cancer. The study could have a significant impact on an upcoming review of federal and international safety regulations for exposure to diesel fumes.

The $11.5-million Diesel Exhaust in Miners Study (DEMS)—run jointly by the National Cancer Institute (NCI) and National Institute for Occupational Safety and Health (NIOSH)-followed 12,315 miners at eight mines in Missouri, New Mexico, Ohio, and Wyoming. An industry coalition denounced the study as flawed almost from the beginning and took the government to court several times. The industry coalition won a court order in 2001 after the government mishandled a procedural filing, forcing scientists to turn over all data and drafts of research papers before publication, for a 90-day review period.

After a year-long process of peer review, the DEMS scientists recently turned over to industry and others copies of two major papers they planned to publish in the Journal of the National Cancer Institute. The mining coalition made no official reply, but in mid-February, as the 90-day waiting period began to wane, Henry Chajet, a Washington D.C.-based lawyer and lobbyist for the Mining Awareness Resource Group (MARG), a party in the court cases, sent a letter to at least four science journals warning them that they risked unspecified consequences if they published the study. (For more on Chajet's letter, and the background of the case, see this post.)

Today marks the 91st day after the DEMS scientists submitted to JNCI. With the legal case still ongoing (it's currently on appeal in a federal court in New Orleans) and the possibility of future complications, DEMS scientists wasted no time publishing either paper (available here and here; NCI and NIOSH also summarized the results here and here).

Debra Silverman, an NCI epidemiologist and lead author of one of the DEMS papers, is the only original scientist still working on DEMS since its inception in 1992. While she said industry groups often challenge workplace studies, "In my career, I never encountered anything like this case. ... This one was longer and harder. It's maybe record-setting, I'm not sure."

In lieu of commenting directly, Chajet issued a statement expressing "disappointment" and claiming that the government scientists never did turn over all the data and documents they should have before publication. He accused DEMS of violating congressional directives and court orders, and criticized the study for being "11 years overdue and $9 million over budget."

The two JNCI papers look at complementary aspects of the DEMS data. The first, a cohort-analysis paper run by NIOSH, looked at all deaths among the miners, from lung cancer as well as other causes. The second, a case-control analysis paper run by Silverman and NCI, focused on lung cancer victims alone, and controlled for smoking, other respiratory diseases, and previous employment in high-risk fields. Both studies found consistent and significant results: a threefold increased risk for lung cancer overall, and a fivefold increased risk for miners most heavily exposed to diesel exhaust. (JNCI also ran an editorial about the study.)

The timing of the release of DEMS data is critical because two prestigious groups, the International Agency for Research on Cancer and the U.S. National Toxicology Program are set to review their standards on the health risks of diesel exhaust. Their decisions could have financial consequences for many users of diesel engines, particularly in lawsuits claiming harm.

While NIOSH and NCI said in a joint statement that "it will be up to the regulators to determine whether the current acceptable level should be lowered," they added that the DEMS results "should be broadly applicable to other workers with similar levels of exposure to diesel exhaust."

The DEMS study was considered groundbreaking both because it controlled for factors like smoking, and because it selected mines that produce non-metallic substances such as limestone, potash, and salt. These mines do not expose miners to potential carcinogens like asbestos, radon, and silica, which therefore allowed DEMS to better isolate the effects of working near diesel-fueled machinery in enclosed spaces.

About her 20-year ordeal to get the study published, Silverman said, "It was so important to the public health that it was worth enduring the challenges." She added, "It's a very good day for us."