PARP1 and breast cancer: Additionally, BSP may promote breast cancer cell proliferation by upregulating SMAD family member 4 (SMAD4) expression18 and Poly(ADP-Ribose) Polymerase 1 (PARP-1) activity.123 Though typically tumour suppressive,126 SMAD4 enhances the proliferation, migration and invasion of breast cancer cells in vitro,18 thereby promoting breast cancer progression.