The present invention provides methods of treatment of cancer patients having deficiency in at least one non-BRCAl/2 gene involved in the homologous recombination repair (HRR) pathway with a poly(ADP-ribose) polymerase (PARP) inhibitor such as niraparib. In particular, cancer patients having a deficiency in at least one gene selected from the group consisting of BRCAl, BRCA2, ATM, ATR, BAPl, BARDl, BLM, BRIPl, MREl l A, NBN, PALB2, RAD51, RAD51B, RAD51C, RAD51D, RAD52, RAD54L, XRCC2, TP53, or RBI can benefit from treatment with niraparib.