These findings suggest that FLT1 activation in human breast tumor cells (pre-treatment) is significantly associated with a higher risk of progression on PARPi, and thus pFLT1/FLT1 status in human breast tumors with BRCA1/2 or PALB2 mutations could serve as a biomarker to stratify patients for benefit from combination treatment with PARPi and FLT1 blockade. Here, FLT1 is linked to breast neoplasm.