To learn about the role of PI3Kγ on HCC initiation by DEN in obese mice, we injected 16-week-old genetically obese ob/ob mice and ob/ob-PI3Kγ-/- mice with 50 mg/kg of DEN, a dose of carcinogen not sufficient to cause HCC in adult mice unless given in association with a tumour promoter such as obesity (Fig. 1H)19ob/ob mice and ob/ob-PI3Kγ-/- mice have been previously characterised,13 and by the age of 16 weeks (the initiation time-point), these mice display similar insulin sensitivity, liver steatosis, and metabolic inflammation.13 This evidence concerns the gene INS and obesity due to melanocortin 4 receptor deficiency.