The IGF signalling pathway was also significantly represented, as found in our previously reported LI phospho-PR gene signature.26 Notably, we observed a decrease in  known ER/PR interactor, IGF1Rβ, in brain metastatic lesions relative to primary PDX tumours, while levels of the IGF system adapter protein IRS-1 were unchanged in bone lesions but modestly elevated in brain lesions. This evidence concerns the gene IRS1 and neoplasm.