The IARC classification scheme

IARC have a five-point scale for classifying agents in their monographs:

Group 1	The agent is carcinogenic to humans
Group 2A	The agent is probably carcinogenic to humans
Group 2B	The agent is possibly carcinogenic to humans
Group 3	The agent is possibly carcinogenic to humans
Group 4	The agent is possibly carcinogenic to humans

Note that IARC say: "The terms probably carcinogenic and possibly carcinogenic have no quantitative significance and are used simply as descriptors of different levels of evidence of human carcinogenicity, with probably carcinogenic signifying a higher level of evidence than possibly carcinogenic."

IARC have quite complicated but precise rules for deriving the overall classification from the separate classifications of the animal and human evidence. We summarise them here. We colour each box according to the normal classification it produces. Where there are alternative classifications, we list these in brackets - these often have to do with mechanistic evidence which is not captured in either the human or animal evidence, and there are one or two further exceptions as well which don't fit neatly in this presentation.

		Animals
		Sufficient	Limited	Inadequate	Suggesting Lack
humans	Sufficient	1	1	1	1
	Limited	2A (1)	2B (2A)	2B (2A)	2B (2A)
	Inadequate	2B (1, 2A, 3)	3 (2B)	3	3 (4)
	Suggesting Lack	3 (1)	3	3	4

On this same grid, the following version shows where EMFs are classified (more):

		Animals
		Sufficient	Limited	Inadequate	Suggesting Lack
humans	Sufficient	1	1	1	1
	Limited	2A (1)	2B (2A)	ELF magnetic fields	2B (2A)
	Inadequate	2B (1, 2A, 3)	3 (2B)	ELF electric fields	3 (4)
	Suggesting Lack	3 (1)	3	3	4