CLDN4 and head and neck squamous cell carcinoma: Across all cancer types, CLDN4 expression was generally elevated in tumour tissues relative to normal counterparts, with the exception of head and neck squamous cell carcinoma (HNSC), kidney renal clear cell carcinoma (KIRC), sarcoma (SARC) and skin cutaneous melanoma (SKCM) (Figure S5b).