CLDN1 and malignant colon neoplasm: Thus, the high levels of claudin 1 expression in some basal-like breast cancers has led to further speculations that claudin 1 may be a tumor-facilitator in this breast cancer subtype [83], as has been shown for claudin 1 in melanomas, colon cancer, and oral squamous cell carcinomas [45,47,66,67,71].