Immunological Significance of the ICI–PIT–ICI Sequence in Recurrent Oral Cancer: A Narrative Review with Illustrative Cases

Immune checkpoint inhibitors (ICIs) have improved clinical outcomes in recurrent or metastatic head and neck squamous cell carcinoma (HNSCC), including oral squamous cell carcinoma (OSCC). However, many patients eventually develop resistance to systemic therapy, highlighting the need for novel strategies that can restore or sustain antitumor immunity. Near-infrared photoimmunotherapy (PIT) has emerged as a tumor-selective locoregional treatment that not only induces targeted tumor cell death but also promotes antitumor immune activation through immunogenic cell death. This narrative review summarizes current evidence regarding PIT for recurrent oral cancer and explores the immunological rationale for sequential ICI–PIT–ICI therapy (ICI–PIT–ICI sequence). Within this framework, PIT-induced tumor antigen release and inflammatory activation may reinitiate elements of the cancer-immunity cycle, whereas continued PD-1 blockade may help sustain newly activated tumor-reactive T-cell responses. To illustrate this concept, we present two cases of recurrent oral cancer treated with the ICI–PIT–ICI sequence. Both patients achieved durable clinical and radiological complete responses following PIT and subsequent nivolumab continuation. Longitudinal analyses of peripheral immune surrogate markers demonstrated a biphasic temporal pattern characterized by transient increases in inflammatory markers, including neutrophil-to-lymphocyte ratio, C-reactive protein, platelet-to-lymphocyte ratio, and systemic immune-inflammation index, followed by recovery trends in absolute lymphocyte count and lymphocyte-to-monocyte ratio during continued PD-1 blockade. These observations support the biological plausibility of PIT as an immune-modulating intervention with potential immune-reprogramming effects. Although hypothesis-generating, the ICI–PIT–ICI sequence may represent a promising strategy integrating locoregional tumor destruction with systemic immune modulation in recurrent oral cancer. Further prospective studies incorporating peripheral and tissue-based immune profiling are warranted.