Radiotherapy-Associated Pain in Head and Neck Cancer: From Clinical Burden to Neuroimmune Modulator.

Radiotherapy-associated pain is among the most common and debilitating complications in head and neck cancer. Although historically viewed primarily as a treatment-related adverse effect, growing evidence suggests that pain is deeply intertwined with tumor biology, immune remodeling, and therapeutic outcomes. At the same time, recent advances in cancer neuroscience have identified sensory nerves as active components of the tumor microenvironment (TME), capable of influencing antitumor immunity through complex neuroimmune crosstalk. These observations raise the possibility that radiotherapy-associated pain is not merely a clinical symptom but also a biological indicator of dynamic changes within the tumor immune microenvironment (TIME). In this review, we outline the major clinical manifestations of radiotherapy-associated pain in head and neck cancer, including inflammatory or mucositis-related pain, neuropathic pain, and long-term chronic pain, with emphasis on their underlying biological features and potential therapeutic relevance. Given that oral mucositis is the dominant source of acute radiotherapy-associated pain in head and neck cancer, we further summarize evidence-based preventive and supportive strategies, including photobiomodulation, mucosal barrier-forming agents, anti-inflammatory mouthwashes, nutritional interventions, pain control, and multidisciplinary oral care. We further discuss how radiotherapy reshapes the TIME through mechanisms such as immunogenic cell death, activation of the cGAS-STING pathway, vascular and stromal remodeling, and regulation of lymphoid compartments, while also triggering compensatory immunosuppressive responses. Preclinical and translational studies suggest that nociceptive signaling pathways may modulate T-cell function, myeloid-cell activity, and immune-evasive programs. Through these neuroimmune interactions, radiotherapy-induced neural injury and persistent pain may contribute to the establishment of an immunosuppressive, wound-like microenvironment that ultimately affects treatment response and tumor progression. Finally, we discuss the translational significance of incorporating pain phenotyping into combined radiotherapy and immunotherapy strategies for head and neck cancer. Opioid-sparing multimodal analgesia, neuromodulation, and neuroimmune-targeted interventions may represent promising approaches to simultaneously improve symptom control and antitumor immunity. We propose that radiotherapy-associated pain may be considered a candidate neuroimmune phenotype rather than a passive adverse event, providing a new conceptual framework for precision management and translational research in head and neck cancer.