MPO and Splenomegaly: Histopathological analysis of moribund animals of PtenΔ/Δ, PtenΔ/Δ;p110αΔ/Δ and PtenΔ/Δ;p110δ−/− mice at 20–40 days post pIpC showed that they developed massive splenomegaly with a marked increase in cells expressing myeloperoxidase, a marker used to detect leukaemic cells of the myeloid lineage, in both the spleen and liver (Supplementary Fig. 2a), confirming MPN development in these mice.