When BRCA1-KO fibroblasts (see above) were exposed to different types of cancer sera, regardless of their origin (e.g., breast cancer, lung cancer or lymphoma), they always acquired a malignant epithelial phenotype compatible with a lower gastrointestinal tract differentiation (CK7−/CK20+/CDX2+), whereas PTEN-deficient MCF10A cells exposed to the same patients’ sera consistently acquired a malignant phenotype suggestive of upper gastrointestinal tract differentiation (CK7+/CK20−/CDX2−) [183]. This evidence concerns the gene CDX2 and breast cancer.