Predictors of therapeutic response and pain after near-infrared photoimmunotherapy in head and neck cancer

Near-infrared photoimmunotherapy (NIR-PIT) has been approved by the Japanese national health insurance for approximately five years, and clinical experience has steadily accumulated. However, reports analyzing treatment outcomes and pain-related factors remain limited. This study aimed to identify predictors of therapeutic response and pain following NIR-PIT. This retrospective cohort study included 25 patients who underwent NIR-PIT for head and neck cancer between January 2021 and June 2025. Lesion diameter and thickness were evaluated in relation to complete response (CR), and the frequency and predictors of post-treatment pain were assessed. Among 22 evaluable patients, eight achieved CR. Lesions with a shorter longest diameter and thinner thickness were significantly associated with higher CR rates ( p = 0.011 and p = 0.024). Moderate-to-severe pain (Numerical Rating Scale ≥4) occurred in 18 of 48 treatment cycles (37.5%) but was significantly less frequent in patients with a history of reconstructive surgery ( p = 0.017). NIR-PIT demonstrated particularly favorable efficacy for short, thin lesions, suggesting that early introduction of treatment may be associated with improved therapeutic outcomes. A history of reconstructive surgery was associated with reduced post-treatment pain, highlighting the importance of individualized treatment and pain management strategies in head and neck cancer patients undergoing NIR-PIT.