PTN and breast carcinoma: On the one hand, studies have found that a low number of breast cancer cases have detectable expression of PTN, while normal breast tissue does not express PTN, while on the other hand, PTN gene expression could play a role in the invasive and/or metastatic behaviour of cell lines or the original tumours the cell lines were obtained from, and targeting PTN with a dominant negative PTN reversed the malignant phenotype of human breast cancer cells in vivo [20, 21].