Our findings that GT3-INCP interacted with GATA3, a GATA family transcription factor that is key to mammary gland development and an essential lineage-specific dependency of ER+ luminal BC, to coregulate the expression of BC susceptibility genes and/or the genes key to the growth/proliferation of ER+ BC cells, demonstrate a lncRNA-encoded protein as an integrated component of a master transcriptional regulatory network that drives the aberrant transcription in cancer, underscoring the underappreciated and important role of lncRNA-encoded proteins in transcriptional regulation. Here, QRSL1 is linked to breast cancer.