Is there any evidence for efficacy of using a PARP inhibitor in metastatic triple negative breast cancer who progressed on platinum therapy with BRCA-2 variant of unknown clinical significance on molecular testing?  

The main recent PARPi trials (OlympiAD, Embraca) enrolled women with known or suspected pathogenic germline mutations so the efficacy in true VUS patients is not known. There are efforts to try and predict the effect of VUS mutations on BRCA function (Woods et al Genomic Med 2016), but we don't know...