PGR and breast cancer: Although phenotypically similar to BRCA1 mutant breast cancers, TNBC are heterogeneous and lack of expression of ER, PR and HER2 is not a good predictor of homologous recombination repair (HRR) status [293] Prognostic and predictive biomarkers of response for TNBC are obvious gaps which need to be addressed [294], complemented by an expanded and representative panel of fully characterised tumour cell lines and models [295].