Interleukin-18 as a Potential Biomarker for Radiotherapy-Related Pain in Breast Cancer: Implications for Personalized Pain Management

Background: Adjuvant RT remains a standard therapy for breast cancer, reducing recurrence risk and improving survival; however, it can also induce side effects, including pain. Inflammasome-related biomarkers, such as interleukin-18 (IL-18), play a role in inflammation-mediated pain, and we hypothesize that IL-18 may serve as a potential biomarker for breast cancer RT-induced pain. Methods: The association between IL-18 and pain was assessed among breast cancer patients receiving adjuvant RT. Plasma IL-18 protein concentration was quantified before and after RT using Ella SimplePlex technology (Biotechne). Clinically relevant pain outcomes included pre-RT pain (pain score ≥ 4), post-RT pain (pain score ≥ 4), and RT-related pain (increase in pain from <4 pre-RT to ≥4 post-RT). Multivariable logistic regression assessed the association between IL-18 and pain outcomes, adjusting for demographic and treatment-related factors. The joint effect of IL-18 and obesity on pain were also explored. Results: Patients in the highest pre-RT IL-18 quartile experienced higher odds of both post-RT pain (OR = 2.36, 95% CI: 1.15–4.87) and RT-related pain (OR = 2.73, 95% CI: 1.20–6.26). IL-18 levels increased from pre-RT to post-RT with a mean change of 0.07 (SD = 0.35). In addition, patients with elevated pre-RT IL-18 levels and obesity experienced the highest odds of post-RT pain (OR = 3.97, 95% CI: 1.98–7.98) and RT-related pain (OR = 2.84, 95% CI: 1.32–6.09), suggesting a potential combined effect. Conclusions: Elevated pre-RT IL-18 levels were associated with an increased risk of pain following adjuvant RT, particularly in breast cancer patients with obesity. Thus, IL-18 may serve as a potential biomarker for identifying patients at increased risk for RT-related pain and informing treatment decision.