PRL and breast carcinoma: 1992), and breast cancer cells of epithelial origin (Ginsberg and Vonderhaar 1995). The 16K PRL isoform is produced as a result of proteolytic cleavage of PRL by cathepsin D, matrix metalloproteinases, or bone morphogenic protein (Clapp et al. 2006). The 16K PRL isoform has inhibitory effects on angiogenesis and tumorigenesis, whereas the major PRL isoform is involved in lactation and reproduction (Bernard et al. 2015).