Rank signaling regulates mammary gland development and epithelial cell differentiation. Rank receptor is expressed by mammary basal and luminal populations, but unlike that of luminal, the contribution of basal Rank signaling to mammary gland homeostasis remains poorly studied. Combining timely-regulated, basal-specific Rank expression with lineage tracing strategies we unveiled that Rank signaling controls basal cell identity in postnatal mammary glands. Enhanced basal Rank disrupts basal and luminal cell identity, resulting in aberrant luminal-like differentiation of basal cells, defective lactation and the appearance of premalignant lesions composed of a basal-derived hybrid population with luminal/alveolar features, which ultimately generates basal and luminal breast adenocarcinomas. Mechanistically, phospho-proteomic, transcriptomic and chromatin analyses support that basal Rank activation triggers the loss of tumor suppressive epigenetic regulators, leading to chromatin remodeling, disruption of basal identity and tumorigenesis. We uncover a basal Rank gene signature that can be predictive of progression from in situ to invasive adenocarcinomas and associates with poor prognosis in breast cancer patients, particularly in those diagnosed with luminal adenocarcinomas, underlining the clinical relevance of our findings. Our results reinforce the idea that basal lineage infidelity triggered by Rank signaling contribute to generation from pre-invasive lesions and transition to invasive breast cancer.