PIK3CA and breast cancer: PARP inhibitors further synergize with inhibitors of the PI3K pathway, as shown in BRCA-proficient TNBC, BRCA1 mutated breast cancer mouse models, PIK3CA mutated ovarian cancer cells, and PTEN mutated endometrial cancer cells (Ibrahim et al. 2012; Juvekar et al. 2012; Wang et al. 2016b; Philip et al. 2017).