Trial of Rucaparib in Patients With Metastatic Hormone-Sensitive Prostate Cancer Harboring Germline DNA Repair Gene Mutations

With respect to germline mutations, a recent study found that the incidence of inherited DNA-repair gene alterations in metastatic prostate cancer to be significantly higher (11.8%) than in both men with localized prostate cancer (4.6%) and in the general population at large (2.7%). Specifically, mutations in 7 genes (ATM, BRCA1, BRCA2, CHEK2, PALB2, RAD51D, GEN1) were significantly enriched in patients with metastatic prostate cancer compared to the general population. These findings suggest that a subset of men are more likely to develop metastatic prostate cancer (i.e. those with germline mutations in DNA-repair genes) and may potentially benefit from PARPi therapy. The clinical activity of PARPi in patients with DNA-repair mutations and metastatic prostate cancer has now been established. Focusing specifically on patients with a germline mutation in a pre-specified group of DNA-repair genes, we hypothesize that targeted therapy with PARPi should be sufficient to induce a clinical response irrespective of hormonal (castration-sensitive or castration-resistant) status. Our hypothesis is based largely on the data from Mateo et al showing a clinical response rate of 88% in a heavily pre-treated population of mCRPC patients with a DNA repair mutation, with the most pronounced responses being in men with germline inactivation. For men with mHSPC, this trial would also provide an alternative to ADT. Identification of a non-hormonal based therapy is warranted as ADT is associated with a shorter time to castration resistance in men harboring a germline DNA repair mutation versus those with intact DNA repair. However, given that primary ADT (in mHSPC) is a standard first-line therapy, all patients on trial must be ineligible for or decline standard-of-care hormonal treatment. For patients with mHSPC who do not respond to PARPi, we will build safety rules into the trial design to take patients off study at first signs of progression. Primary ADT (mHSPC) would still remain a treatment option upon progression.