<p>Non-genetic resistance of cancer remains poorly understood in clinical research and practice. To better understand resistant cancer cell heterogeneity, we isolated a novel riboflavin⁺NOTCH1⁺ population from cisplatin-naïve and -resistant lung cancer cell lines and patient specimens with or without immunotherapy and chemotherapy. This population was also identified as <i>SLC52A2</i> (one of the riboflavin transporters)⁺<i>NOTCH1</i>^<i>+</i> cells in single-cell RNA sequencing (scRNA-seq) data derived from advanced lung tumors before therapy. Despite its therapy-naïve origin, the population, designated as stably resistant cancer cells (SRCC), exhibited the epithelial state, innate and stable resistance to therapy (chemotherapy, targeted therapy and immunotherapy), cell dormancy, elevated reactive oxygen species (ROS), and anti-apoptotic and anti-ferroptotic survival. These cellular and molecular characteristics distinguished SRCC from other resistant populations, including cancer stem-like cells (CSC), epithelial-mesenchymal transition (EMT) cells, and drug-tolerant persisters (DTP). The non-canonical NOTCH1 pathway, but not the inactivated canonical NOTCH1 pathway, played a critical role in the resistance of SRCC. Specifically, it modulates cell cycle, iron metabolism, EMT, and ferroptosis vulnerability in SRCC at the transcriptional level. It also controls the initiation of ferroptosis in lysosomes via a posttranslational NOTCH1-AKT-BAX axis. Inhibition of the non-canonical NOTCH1 pathway re-sensitizes these dormant and resistant cells to cisplatin-induced cell death in vitro and in vivo, including ferroptosis, apoptosis, and necroptosis. Our study contributes to a deeper understanding of cancer resistance and promotes the development of more effective therapeutic strategies against resistant cancer cells.</p><p></p>