Heterozygous BRCA1 Deletion, but not Complete BRCA1 Loss, Confers Resistance to Androgen Deprivation Therapy in Prostate Cancer

BRCA1 is biallelically deleted or mutated in at least 1.9% of prostate tumors, but whether BRCA1 deficiency influences resistance to androgen deprivation therapy (ADT) and prostate cancer development remains elusive. Here we surprisingly find that in human, BRCA1 heterozygous deletion is observed in approximately 13% of human prostate cancers, is more prevalent in neuroendocrine prostate tumors and predicts worse survival than BRCA1 homozygous deletion. In mice, we show that Brca1 heterozygosity (HET) but not Brca1 full inactivation (KO) accelerates early tumor development, invasion and resistance to ADT in Pten-null prostate tumors. Furthermore, pre-malignant tumors and organoids derived from Brca1 HET mice undergo neuroendocrine differentiation and exhibit elevated levels of the unfolded protein response potentially as a pro-survival mechanism, but not those of Brca1 KO. Our findings thus provide important insights into clinical management of prostate cancer patients, suggesting that patients heterozygous for Brca1 are prone to developing resistance to ADT and should be treated differently from patients with complete Brca1 loss. 24 samples were sequenced, including mouse prostate tissues and organoids of different genotypes and grown in different conditions. Samples can be grouped into biological replicates or triplicates