Pain signaling via sensory neurons drives breast cancer progression through neuropeptide release and κ-opioid counter-regulation.

Severe pain in patients with breast cancer is associated with poorer survival outcomes, yet the mechanisms linking nociceptive signaling to tumor progression remain unclear. In a clinical cohort, breast cancer patients whose moderate or severe pain improved under specialized palliative care exhibited significantly longer survival than those with persistent pain. Serum levels of calcitonin gene-related peptide (CGRP) and substance P (SP), neuropeptides that can be released from sensory neurons, were elevated in breast cancer patients with uncontrolled pain, correlating positively with pain intensity and negatively with overall survival. In vitro, supernatants from depolarized human iPSC-derived sensory neurons containing CGRP, SP, and the endogenous κ-opioid receptor (KOR) ligand dynorphin attenuated docetaxel efficacy, promoted epithelial-mesenchymal transition, and enhanced migration in human triple-negative breast cancer (TNBC) cells, accompanied by Gi protein-coupled activation of the PI3K-Akt signaling pathway. In vivo, optogenetic activation of sensory neurons significantly accelerated tumor growth following orthotopic transplantation of murine TNBC cells, whereas combined blockade of CGRP and SP receptors suppressed this effect. Similarly, in patient-derived xenograft models of TNBC, dual receptor blockade effectively abrogated tumor progression. Conversely, in vitro treatment with dynorphin enhanced the cytotoxic efficacy of docetaxel, accompanied by the inhibition of PI3K-Akt signaling, whereas in vivo administration of the peripherally restricted KOR agonist nalfurafine methiodide markedly suppressed tumor growth. These findings establish a bidirectional neural-tumor axis in breast cancer progression. Therapeutically, combined blockade of CGRP/SP signaling with peripheral KOR agonism may present a novel strategy to enhance chemotherapy efficacy in TNBC patients.