Breast cancer is very diverse illness. Treatment of breast cancer that contain genetic mutations and DNA repair deficiencies with PARP inhibitors is showing a promising result. BRCA 1 and BRCA 2 patients respond very well to this treatment. Also, studies suggesting treatment used in HER2 negative and hormone receptor positive patients combined with immunotherapy can be effective. Not to mention that PARP inhibitors target cells with defective DNA repair and spares healthy cells so this lessens the possibility of unpleasant side effects.