BRCA1 and breast cancer: To validate our preclinical findings, we performed pFLT1 and FLT1 immunostaining on tissue specimens that were obtained prior to PARPi treatment from 10 breast cancer patients harboring mutations in the BRCA1/2 or PALB2 DNA damage response (DDR) genes (Fig. 7; Appendix Fig S2A,B; and Appendix Table S1).