A Neuron Projection Guidance Signature Associates with Immune-Cold Tumor Microenvironment and Poor Outcomes in Breast Cancer

Background: Neural involvement in the tumor microenvironment (TME) has increasingly been recognized as a regulator of cancer aggressiveness. However, its characterization in breast cancer remains a challenge due to very low nerve density in this cancer type. This study investigates the clinical relevance of cancer-medicated nerve recruitment activity in the TME of breast cancer patients. Methods: Transcriptomic and clinical data from 9017 breast cancer patients across multiple cohorts were analyzed. A Neuron Projection Guidance (NPG) score generated by GSVA of a MSigDB gene set was used to quantify nerve recruitment activity. Patients were dichotomized by cohort-specific medians. Results: The NPG score was associated with axonogenesis-related gene expressions. NPG-high tumors exhibited lower cell proliferation, indicated by less Ki67 gene expression, and less enrichment of proliferation-related Hallmark gene sets. NPG-high tumors revealed significantly lower mutational burdens and neoantigen loads, which were consistent with an immune-cold TME, characterized by lower infiltration of immune effector cells, decreased cytolytic activity, and suppressed immune-related pathways. NPG scores were higher in patients who did not achieve pathological complete response after neoadjuvant chemotherapy. Moreover, high NPG scores were associated with poorer survival. These associations were observed in triple-negative breast cancer (TNBC), but not consistently in ER+/HER2− nor HER2+ subtypes. Conclusions: These findings reveal a previously unrecognized tumor-neuronal cross-talk in TNBC biology, which associates with an immune-cold TME, reduced chemotherapeutic efficacy, and unfavorable clinical outcomes. Such a network has potential implications for risk stratification and therapeutic decision-making in TNBC.