Substances, mixtures and exposure circumstances in this list have been classified by the IARC as Group<unk> : The agent (mixture) is probably carcinogenic to humans. The exposure circumstance entails exposures that are probably carcinogenic to humans. This category is used when there is limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals. In some cases, an agent (mixture) may be classified in this category when there is inadequate evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals and strong evidence that the carcinogenesis is mediated by a mechanism that also operates in humans. Exceptionally, an agent, mixture or exposure circumstance may be classified in this category solely on the basis of limited evidence of carcinogenicity in humans. 
Further details can be found in the IARC Monographs.
List of IARC Group 2A carcinogens
List of IARC Group 2B carcinogens
List of IARC Group 4 carcinogens
List of IARC Group 3 carcinogens
List of IARC Group 1 carcinogens
List of cancer mortality rates
List of cancer clusters
List of cancer types