CLDN6 and neoplasm: In the paired primary-metastasis cohort, Claudin-6 was highly expressed in 19% of primary tumours and, of these, 77% maintained high expression in at least one corresponding metastatic lesion.<h4>Conclusions</h4>Our study identified Claudin-6 as an independent prognostic marker in EC and as a potential target for ADCs, particularly in serous and carcinosarcoma subtypes.