Knockdown of Claudin-8 (CLDN8) Indicates a Link Between Breast Cancer Cell Sensitivity to Chemotherapeutics and Reveals a Potential Use of CLDN8 as a Molecular Diagnostic and Target for Therapy.

Breast cancer is a heterogeneous disease, and treatment resistance remains a critical challenge. Claudin-8 (CLDN8), a tight junction protein, has emerged as a potential indicator of therapeutic response and prognosis in breast cancer patients. In this study, we evaluated CLDN8 as a predictive biomarker and a potential therapeutic target. We analyzed CLDN8 gene expression in breast cancer patient cohorts to assess its association with clinical outcomes and response to therapy. We also established breast cancer cell models with altered CLDN8 expression to examine its effects on cell behavior and drug sensitivity. High CLDN8 expression was significantly associated with improved disease-free survival, particularly in estrogen receptor-negative patients (p = 0.007), suggesting a favorable prognostic role. Notably, tumors with elevated CLDN8 showed better outcomes in patients treated with surgery alone or endocrine therapy, whereas in those receiving chemotherapy (including neoadjuvant) or anti-HER2 therapy, high CLDN8 levels were paradoxically linked to poorer survival and therapy resistance. In vitro, CLDN8 knockdown reduced sensitivity to endocrine treatments, HER2-targeted agents, and chemotherapeutic drugs, mirroring clinical patterns. In conclusion, our findings identify CLDN8 as an important prognostic factor in breast cancer and as a novel predictor of treatment response. These results underscore the potential utility of CLDN8 status in guiding personalized therapy and highlight CLDN8 as a candidate target for overcoming treatment resistance in breast cancer.