Finally, to confirm that FOXC1 levels were indeed elevated in Luminal B but not HER2+ PDXs treated with GSK-126, we performed qRT-PCR on breast tumour samples at endpoint and confirmed a significant upregulation of FOXC1 transcript levels in GSK-126 treated HCI003 Luminal B but not 1991 HER2+ PDXs (Fig. 7d). Here, ERBB2 is linked to breast neoplasm.