PTEN-deficient MCF10A cells, a human mammary epithelial cell line, that has not shown to be tumorigenic (herein called MCF-PKO cells)27,28,31,33 was treated with sera of cancer patients and its hypothesized malignant transformation was compared to the transformation obtained in a positive control group made of BRCA1-mutated fibroblasts (herein called Fibro-BKO cells) treated mostly with the same type of cancer sera. Here, PTEN is linked to cancer.