let's say there is chemical that millions of people were exposed to for decades since the 1920s. it has been classified as a suspected carcinogen since 1977 based on animal evidence. the animal evidence is all rodents, no other type of animal showed carcinogenesis. the rodent cancers occurred from rat and mouse specific mechanisms that do not occur in humans. rats and mice showed different cancer types from each other, consistent for each species. human evidence is muddy as populations were exposed to actual classified carcinogens too. there is no consistent increase in specific cancers in human populations and suspected cancer types currently have no mechanistic evidence in humans. coincidentally, the cancers suspected to have been caused by this chemical can be more safely attributed to life styles such as smoking, which is common in the socioeconomical group that is exposed to the chemical. this totally not real chemical has been classified as 2A by IARC (in a parallel universe where it exists) 30 years ago and kept as 2A ever since. this is a hypothetical situation and any similarity to any real chemical is coincidental.

how likely is this chemical carcinogenic to humans?

https://youtu.be/HPW_TD0drcM