Bacon vs cigarettes

There has apparently been a leak from the International Agency for Research on Cancer about their forthcoming assessment of meat. It’s just in the UK papers so far, but I expect it will spread. Here’s an example, from the Telegraph

Bacon, ham and sausages ‘as big a cancer threat as smoking’, WHO to warn
The WHO is expected to publish a report listing processed meat as a cancer-causing substance with the highest of five possible rankings

Presumably what they mean is that IARC is going to classify processed meat as a Group 1 carcinogen. The story is playing on a common misunderstanding of the IARC hazard grades for carcinogenicity.

As I’ve written before, the IARC hazard grades aren’t about the magnitude of the threat. A Group 1 carcinogen is an agent whose ability to cause or promote cancer is well established. To quote the Preamble to the IARC Monographs

A cancer ‘hazard’ is an agent that is capable of causing cancer under some circumstances, while a cancer ‘risk’ is an estimate of the carcinogenic effects expected from exposure to a cancer hazard. The Monographs are an exercise in evaluating cancer hazards, despite the historical presence of the word ‘risks’ in the title. The distinction between hazard and risk is important, and the Monographs identify cancer hazards even when risks are very low at current exposure levels, because new uses or unforeseen exposures could engender risks that are significantly higher.

In the Monographs, an agent is termed ‘carcinogenic’ if it is capable of increasing the incidence of malignant neoplasms, reducing their latency, or increasing their severity or multiplicity.

The ‘five possible rankings‘ mentioned by the Telegraph could also do with some clarification. Effectively, there are three rankings, officially defined as “definite”, “probable”, and “possible”. There’s a “don’t know” ranking for things that haven’t been studied enough to make any assessment. Finally, there’s a largely-hypothetical “probably not” ranking, which has only ever been used once in nearly a thousand assessments.

If the leak is correct, processed meats will be joining alcohol, plutonium, sunlight, tobacco, birth-control pills, and Chinese-style salted fish in Group 1. These aren’t all an equal threat, but the IARC scientists believe all of them are able to cause cancer at the right dose.