BETHESDA, MdThe number of substances known or
reasonably anticipated to cause human cancer now stands
at 218, according to the newly published Report on Carcinogens,
9th edition. The new number represents a total increase of 14
substances over the 8th edition. Sixteen substances were added to the
previous list, and, for the first time, two were removed.
Report on Carcinogens, which Congress first ordered prepared
in 1978, is published every 2 years by the National Toxicology
Program (NTP), headquartered at the National Institute of
Environmental Health Sciences (NIEHS), Research Triangle Park, NC.
The purpose of the report is to identify potential cancer hazards,
and it does not take into account potential benefits of substances.
Some oncologic drugs, for example, are listed because their use can
lead to second cancers.
People should not make decisions concerning the use of a given
drug, or any other listed agent, based solely on the information
contained in the report, NTP warned. Decisions of this
type should be made only after consulting with a physician or other
appropriate specialist about both risks and benefits.
The artificial sweetener saccharin and ethyl acrylate, which is used
in making latex paints and textiles, were both removed from the list
of substances reasonably anticipated to be a human
carcinogen. Saccharin had been listed in the report since 1981
and ethyl acrylate since 1989.
Two decades ago, when saccharin was shown to produce bladder
tumors in rats, it was a prudent, protective step to consider the
sweetener to be a likely human carcinogen, said NIEHS director
Kenneth Olden, PhD, who also heads the NTP. However, our
understanding of the science has advanced and allows us to make finer
distinctions today. Studies now indicate that the rat bladder tumors
arise from mechanisms that are not relevant to the human
As for ethyl acrylate, new studies have shown that the tumors found
in animals developed only when the chemical was given orally in high
concentrations, which resulted in persistent and severe gastric
Saccharin and ethyl acrylate were the first substances removed from
the list since NTP established a formal delisting procedure in 1996.
New on the List
Newly listed in the report and given known human
carcinogen status are environmental tobacco smoke, tobacco
smoking, and smokeless tobacco; consumption of alcoholic beverages;
and solar ultraviolet radiation and exposure to sunlamps and sunbeds
Tamoxifen (Nolvadex) was also added to the list, based on studies
that show the drug causes uterine cancer.
There has been concern expressed that the listing of tamoxifen
in the 9th Report could raise concerns among patients
regarding its use for cancer treatment or prevention, the NTP
said. In this instance, the benefits of exposure to the
substance have been determined by the FDA to outweigh the risks
entailed. . . It is very important that the public and physicians be
aware of potential risks so that they have the necessary knowledge to
weight the benefits versus the risks of using tamoxifen.
Two other new listings are strong inorganic acid mists containing
sulfuric acid, used in the manufacture of isopropyl alcohol, lead
batteries, phosphate fertilizers, soap and detergents, synthetic
ethanol, and pickling and other acid treatments of metals, and dyes
metabolized to benzidine, used mainly for dyeing textiles and paper.
TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) has been proposed for
upgrade to the known to be a human carcinogen category,
but the proposed listing is currently in litigation.
Upgraded to Known Carcinogen
Substances upgraded from the reasonably anticipated list
to known human carcinogen are:
Crystalline silica of respirable size, primarily quartz dust
occurring in industrial and occupational settings.
1,3-Butadiene, used in making synthetic rubber.
Cadmium and cadmium compounds, found in batteries, plastics,
synthetic products, and alloys.
Ethylene oxide, used in making other chemicals and for sterilizing
Six substances were added to the reasonably anticipated list:
Diesel exhaust particulates, based on findings of elevated lung
cancer rates in occupational groups exposed to diesel exhaust,
including railroad, bus garage, and trucking company workers.
Isoprene, a major component of natural rubber used in making
synthetic rubbers and found in tobacco smoke and automobile exhaust.
Chloroprene, used primarily in making elastomer polychloroprene (neoprene).
Phenolphthalein, used as a laboratory reagent and acid-base
indicator, and formerly as an ingredient in over-the-counter laxatives.
Tetrafluoroethylene, used in the production of many polymers.
Trichloroethylene, primarily a degreaser of metal parts and once used
to decaffeinate coffee.