The gene CLDN4 encodes the tight junction proteinClaudin-4 (Clostridium perfringens enterotoxin receptor).Depending on the type of cancer, expression of Claudin-4has been linked to either a better diagnosis or a worseprognosis. In malignant effusions, Claudin-4 hasdemonstrated 99% specificity in differentiating betweenadenocarcinoma and malignant mesothelioma. In amultivariate study of breast cancer, overexpression ofClaudin-4 was able to predict survival on its own since itwas inversely connected with oestrogen receptor staining,linked to poor prognosis, high tumour grade, and Her2expression. An overall lower life survival was shown inluminal breast cancer, where an increase in Claudin-4protein was linked to an increase in tumour grade and Ki-67. Claudin-4 was also overexpressed in basal-like tumours.The presence of Claudin-4 in triple negative breast cancerwas a biomarker that showed a good prognosis, in contrastto the aforementioned breast cancer subtypes. Poordifferentiation was linked to Claudin-4 loss, which wasobserved in 69% of advanced gastric tumours. Inesophageal squamous cell carcinoma, low Claudin-4protein expression was associated with increased T staging,lymphatic metastases, and recurrence risk. Prostate cancerthat overexpresses Claudin-4 may benefit from Claudin-4targeted therapy.