Case report suggests grade 3 ICI-induced inflammatory arthritis may correlate with sustained response to tislelizumab in advanced head and neck carcinoma.

Immune checkpoint inhibitors (ICIs) have emerged as promising treatment strategies in cancer immunotherapy. However, a significant proportion of patients do not respond to these therapies, underscoring the need for reliable biomarkers of treatment responsiveness. Although a potential correlation between the development of immune-related adverse events (irAEs) and favorable response to ICI therapy has been demonstrated, the predictive reliability of irAEs for treatment efficacy remains to be fully established. This report presents a case of advanced unknown primary carcinoma of the head and neck (UPCHN) with rapid disease progression following initial treatment with neck dissection and concurrent chemoradiotherapy. Subsequent administration of a weekly regimen comprising paclitaxel, carboplatin, and cetuximab (PCC) resulted in complete response (CR). Maintenance therapy with cetuximab and tislelizumab was then initiated. After 20 months of sustained CR, the patient developed grade 3 ICI-induced inflammatory arthritis (ICI-IA), necessitating discontinuation of ICI therapy. Notably, the patient remained in complete remission for over 1 year following cessation of ICI therapy, with no clinical or radiographic evidence of tumor progression. This case suggests that the development of ICI-IA reflects an immune hyperactivated state that correlates with long-term antitumor response to tislelizumab. The sustained remission observed in this patient following ICI discontinuation highlights the potential role of irAEs, particularly ICI-IA, as a potential biomarker of ICI efficacy. Further prospective, large-scale studies are warranted to validate these findings and assess their clinical applicability.