PAPPA and neoplasm: Although 4T1.2 cells do not produce PAPP-A, host cells within 4T1.2 tumours do produce PAPP-A [19] and is the likely reason why wtIGFBP4 had no effect on 4T1.2 tumour growth or angiogenesis in that study as host-cell derived PAPP-A will cleave the wtIGFBP4 rendering it unable to sequester IGF.