This 2019 article questioned the paradigm of determining substance carcinogenicity:

“In the absence of robust epidemiological data, the final arbiter of whether a chemical is considered to be a carcinogen or not has been based on the outcome of long-term rodent bioassays. This approach is incompatible with the current knowledge of the etiology of cancer. The current view of the etiology of cancer suggests that it is not useful to consider carcinogenicity as a single hazardous property with its own hazard category.

There is no bright line between carcinogens and non-carcinogens but rather there is a continuum with some chemicals having high potential, some having no potential, and others having potential at a point along the continuum. This continuum exists alongside other adverse effects. One problem is being stuck in the old practice of wishing to reproduce the binary “carcinogen/non-carcinogen” results of the long-term bioassay rather than move to a new paradigm in assessing the chemical’s position on the spectrum of carcinogenic potential.

The two-year bioassay has such high variability (because of the variability of the carcinogenic process it is trying to measure and the interplay between dose limiting toxicity and cell proliferation inducing toxicity) that the outcome of the assay for compounds with low to intermediate carcinogenic potential is little more than a lottery. After half a century, it has only been used to evaluate less than 5% of chemicals that are in use. It is not reproducible because of the probabalistic nature of the process it is evaluating combined with dose limiting toxicity, dose selection, and study design.”

Unscientific research paradigms will eventually collapse because they can’t withstand the scrutiny of the scientific method. Too bad the coauthors didn’t kill off this one while they were still in positions at the US Environmental Protection Agency, World Health Organization, etc.

https://www.sciencedirect.com/science/article/pii/S0273230019300248 “Chemical carcinogenicity revisited 2: Current knowledge of carcinogenesis shows that categorization as a carcinogen or non-carcinogen is not scientifically credible” (not freely available)