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NTP Board Peer Reviews Draft Cancer Reports

By Robin Mackar
March 2009

Wolfe provided a thorough overview of the new RoC process, which substantially increases opportunities for public input. (Photo courtesy of Steve McCaw)

John Bucher, Ph.D., Novak, Linda Birnbaum, Ph.D, and Michelle Hooth, Ph.D.
New NIEHS/NTP Director Linda Birnbaum, Ph.D., second to right, participated actively in the two-day meeting and presented her vision for the NIEHS/NTP as well as budget updates. Sitting with her left to right are John Bucher, Ph.D., NTP Associate Director, Novak and NTP lead scientist for the technical reports, Michelle Hooth, Ph.D. (Photo courtesy of Steve McCaw)

James Sherley, M.D., Ph.D.
James Sherley, M.D., Ph.D., center, was one of the newly appointed members attending a BSC meeting for the first time. Michael Pino, D.V.M., Ph.D., sat to Sherley's left. (Photo courtesy of Steve McCaw)

Chad Blystone, Ph.D. and Grace Kissling, Ph.D.
This was also the first public peer review of a technical report for Chad Blystone, Ph.D., above left. He was the study scientist for the androstenedione technical report and is an IRTA fellow recently hired in the Toxicology Branch as part of NTP's Applied Toxicology and Carcinogenesis postdoctoral training program. Grace Kissling, Ph.D., NTP biostatistician, conversed with Blystone at the meeting. (Photo courtesy of Steve McCaw)

Cesta shown at a recent training class put his new skills to work as he presented pathology slides to the BSC. (Photo courtesy of Steve McCaw)

Report on Carcinogens (RoC)

National Toxicology Program (NTP) reports on five of the nine compounds being considered for listing in the 12th Report on Carcinogens (RoC) were for the first time peer reviewed by the NTP Board of Scientific Counselors (BSC) February 24 in Rodbell Auditorium. Four of the chemicals, including ortho-nitrotoluene, used in the synthesis of some dyes; aristolochic acids, a family of acids used in herbal medicine; captafol, previously used to control fungal diseases in fruits, vegetables and other plants; and riddelliine, a toxic plant component, underwent a thorough, but relatively quick review by the BSC. The majority of the day was spent discussing the weight of evidence presented in the styrene draft substance report.

Styrene is a highly flammable liquid used worldwide in the production of polymers that are incorporated into products such as rubber, plastic, insulation, fiberglass, pipes, automobile parts, food containers and carpet backing. The NTP's preliminary policy decision for listing styrene is that styrene is reasonably anticipated to be a human carcinogen based on limited evidence in humans, sufficient evidence of carcinogenicity in experimental animals and supporting mechanistic data.

"This is the first time we're bringing draft substance profiles from the RoC for peer review to the Board," said Mary Wolfe, Ph.D., director of the NTP Office of Liaison, Policy and Review, during her presentation to the BSC. She outlined the new multi-step scientific review process for the RoC ( and presented the board's charge, which is to determine whether the scientific information cited in each draft substance report is technically correct, clearly slated and supports the NTP's preliminary decision regarding its listing in the RoC. She explained the status of the remaining four RoC candidate substances - cobalt-tungsten carbide powders and hard metals, metalworking fluids, certain glass wool fibers, and formaldehyde - and told the board they would likely be peer reviewing those substances in the next year.

Wolfe also highlighted the multiple opportunities for public input into the process, which was evident at the board meeting. Eight public commenters were provided ample opportunity to offer oral remarks or make presentations regarding the styrene draft substance profile, in addition to providing written comments for the record. Board members also had an opportunity to discuss and deliberate the comments with the public presenters. Representatives from industry included George Cruzan from ToxWorks who spoke on behalf of the Styrene Information Center and James Bus, Ph.D., from Dow Chemical speaking on behalf of the American Chemistry Council Ethylbenzene Panel. They and others shared reasons why they did not agree with the NTP draft listing. A non-scientist voice was also heard from Jay Merrell, who spoke on behalf of Industrial Dielectrics, a business his father started in 1966 that uses styrene-polyester resin to make highly engineered molding compounds. Merrell urged the NTP to do its work carefully, but not to needlessly frighten people about this compound.

The public comments followed a scientific presentation on each compound made by NTP staff. In the case of styrene, RoC Director Ruth Lunn, Dr. P.H., discussed the critical papers and data used by the NTP to recommend listing styrene as reasonably anticipated to be a human carcinogen. Her analysis included human, animal and mechanistic data.

The NTP recommended listing aristolochic acids as known to be human carcinogens based on sufficient evidence from studies in humans and supporting mechanistic data. Captafol, o-nitrotoluene, and riddelliine are recommended to be listed as reasonably anticipated to be human carcinogens.

Each compound reviewed had two to six lead BSC or ad hoc reviewers. Other BSC members also participated in the discussion of each profile. Overall, the BSC provided editorial and thoughtful comments and input on each draft report that the NTP will use to finalize its policy decision regarding the compound's listing in the RoC. The BSC meeting was aptly chaired by Kenneth Portier, Ph.D.

Technical Reports on NTP 2-Year Cancer Bioassays

The following day, the NTP BSC Technical Reports Review Subcommittee completed its independent public peer review of six draft NTP technical reports. These reports are used by regulatory authorities worldwide for developing risk assessments and regulations to establish "safe" levels of chemicals in the environment.

The agents studied included goldenseal root powder, a dietary supplement ingredient; androstendione, a dietary supplement banned in 2004 for over-the-counter sales; Β-myrcene, an ingredient used in the production of scents and flavorings; 2,3',4,4',5-pentachlorobiphenyl (PCB 118), a dioxin-like compound evaluated as part of NTP's program on dioxins; 3,3',4,4'-tetrachloroazobenzene, a contaminant found in herbicides; and tetralin, an industrial solvent. An overview of each report was presented by an NTP study scientist, followed by the committee's peer review. An additional presentation by NTP pathologist Mark Cesta, D.V.M., following the overview of the Β -myrcene report provided more detail about the histopathologic features of the non-neoplastic renal diseases that were seen in the rat studies. All of the agents presented were found to have carcinogenic activity in the rodent models. The draft reports are available online ( The technical report reviews were chaired by Raymond Novak, Ph.D.

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