IARC Carcinogen List
The IARC (International Agency for Research on Cancer) publish a list of known and suspected carcinogens, in a series of Monographs, for details of their work see http://www.iarc.fr/.
Under the IARC carcinogenicity classification, there are Category 1A and 1B, Category 2, and Category 3 Carcinogens.
The list of IARC carcinogens does not match the CLP/ GHS carcinogenic classification (H350, H351), as the Category 3 substances are those which have been reviewed but have not got evidence that they are carcinogenic.
Some Category 2 Carcinogens are included simply because they are carcinogenic if you dose animals with enough (although this is more of a carcinogenic effect through over-exposure, and can occur with otherwise non-hazardous substances); and these types of carcinogens are generally not be included as a CLP or GHS carcinogen.
The current list of IARC Carcinogens (with last download date) is: List_of_IARC_Classifications 22-01-2018 .
Relationship of IARC Carcinogens and CLP Carcinogens
The IARC Carcinogens included within CLP usually hold Harmonised Classifications, and usually comprise the Cat 1 and Cat 2A IARC carcinogens. Cat 2B and Cat 3 have, until recently, not been classified for CLP as Harmonised Classifications.
However, this has recently changed, as in June 2017 ECHA have decided to classify Titanium Dioxide (an IARC Cat 2B Carcinogen) as a Cat 2 Carcinogen by inhalation, H351, under CLP. The decision can be viewed at https://echa.europa.eu/-/titanium-dioxide-proposed-to-be-classified-as-suspected-of-causing-cancer-when-inhaled .
This decision appears to fly in the face of most of the scientific evidence, when interpreted correctly, and appears to be based on politics rather than sound science. The error in interpretation seems to arise from the fact that rats, when exposed to high dust levels of any material, will form tumours. This is simply an effect from “overload”, and not related to the chemistry of the dust. This tumour-forming mechanism is known not to occur in mice, or humans, so there is no reason to use data on tumour formation which only occurs in rats (and not in mice or other tested mammals) as a basis for classifying a substance as a carcinogen to humans. For more information, see http://www.tdma.info/clh-dossier .
There is a suspicion amongst the chemical industry and some toxicologists that some IARC carcinogens have been placed on the list for political reasons, and Titanium Dioxide, Talc, and Carbon Black all fall into this category. Funnily enough, they are all covered by a single IARC Monograph, no 93: http://monographs.iarc.fr/ENG/Monographs/vol93/mono93.pdf . This monograph was published following a meeting in Lyon, France in 2010, and it is the ANSES (the French equivalent of the HSE) who have been pushing for Titanium Dioxide to be classed as a carcinogen under CLP.
The evidence that all three of these chemicals may be carcinogenic is limited, despite high profile lawsuits in the USA around talcum powder, which are still ongoing at the time of writing (June 2017), see https://www.reuters.com/article/us-johnson-johnson-cancer-lawsuit-idUSKBN19B3AV .
However, the decision in the EU to classify titanium dioxide as a Cat 2 carcinogen under CLP has much wider implications, as the Risk Assessment Committee have already said that this decision will be applicable to all other partially soluble low-toxicity particles (PSLTs) which are proposed for classification, meaning that many other solids in powder format may suddenly find that they are classified as Cat 2 carcinogens.
It is important to remember that, as individuals, the decision on whether a substance is or is not carcinogenic is taken at country/EU level; or during the compilation of a REACH dossier, when toxicologists should be involved in interpreting the test data. We should not apply a carcinogenic classification unless a Harmonised Classification exists, or a REACH dossier states that this classification applies, and not assume that everything on the IARC Carcinogen list is automatically a carcinogen.