> A spontaneous tumor incidence of 45% was noted in 360 Sprague-Dawley rats (179 males and 181 females) and a 26% incidence was seen in 254 Swiss mice (101 males and 153 females) used as untreated control animals in an 18-month series of carcinogenesis experiments.
A tiny increase in cancer over a large base rate is going to be tricky to find.
http://cancerres.aacrjournals.org/content/33/11/2768
> A spontaneous tumor incidence of 45% was noted in 360 Sprague-Dawley rats (179 males and 181 females) and a 26% incidence was seen in 254 Swiss mice (101 males and 153 females) used as untreated control animals in an 18-month series of carcinogenesis experiments.
A tiny increase in cancer over a large base rate is going to be tricky to find.