Hazard identification, classification, and risk assessment of carcinogens: too much or too little? – Report of an ECETOC workshop

An international workshop organised by the Centre for chemical safety assessment (ECETOC) was held in September 2019 in Helsinki to explore the scientific limitations of the current ‘binary’ carcinogenicity classification scheme that categorises substances as either carcinogenic or not, regardless of mechanism, and identified opportunities to overcome these limitations.

Cancer is a serious, potentially life-threatening disease and it is vital that people do not develop it through exposure to chemicals. To ensure public protection, regulators rely mainly on tests (such as a 2-year study using rats or mice called the ‘rodent bioassay’) and classification schemes to label chemicals as carcinogens. Many laws, for example around food, agriculture and cosmetics, ban the use of any substance classified as a carcinogen in this way.

While the intent of the original classification systems was to protect public health, in reality many chemicals are now labelled as carcinogens that do not, in fact, raise any concern for human health when exposures are kept below globally accepted levels. This has huge economic implications for both industry and consumers.

The workshop concluded that classification based on the rodent bioassay was a poor model for predicting human carcinogenicity, so should be abandoned. Instead, innovative testing strategies based on, for example, cell culture tests, computer modelling, and shorter-term toxicity studies may be useful to determine if a substance is likely to be carcinogenic. A prerequisite for this is that these tests are conducted under conditions relevant to human health. This new testing strategy will also minimise animal testing.