BRCA1 and breast cancer: Gemcitabine primarily causes Poly (ADP-ribose) polymerase (PARP) degradation through autophagy-regulated processes rather than apoptosis [51], which is why the results of single-agent gemcitabine chemotherapy are significantly improved by adding a PARP inhibitor in BRCA-1-deficient pancreatic and breast cancer cell lines [52,53,54].