This is a good question. First take a look at the American Cancer Society page that describes how compounds are tested (or not tested) to determine if they are carcinogenic.
https://www.cancer.org/cancer/risk-p...arcinogen.html
Second, realize that the testing is done for a relatively short term with very high doses. This type of testing can skew results at times. However, short of doing lifetime testing on humans, it is the best we can do right now.
Finally, everyone has a different sensitivity to the variety of agents out there. After benzene was determined to be a carcinogen, my father (who had washed his hands in benzene at the end of each workday for 30 years) said "I guess I am not sensitive to benzene." He lived to 93 and died of pneumonia.
Bottom line, if your family history has a lot of cancer, you might want to be careful. Given my family history, I am guessing that I will not die of cancer.