WNT1 and neoplasm: The tumor formation speed in both cohorts of mice is markedly faster than that in AAV-P– and Lenti-PIK3CAH1047R–infected mice without the MMTV-Wnt1 transgene (Fig. 4B) or in MMTV-Wnt1 mice without viral injection (31, 43), demonstrating that PI3K and Wnt1 collaborate to promote mammary tumorigenesis.