ESR1 and breast neoplasm: Bennett et al. then presented evidence that GIP-8 was orally-active in the induction of the nitrosourea-induced rat breast tumors and that GIP-8 interfered with the phosphorylation of the human estrogen receptor (ER) at serine-118 and also with phosphorylation of p53 at serine-15 and serine-392 [24].