Our studies of growth factors and their signal transduction connected the ALK receptor with the growth factor pleiotrophin (PTN): We had purified and characterized PTN from supernatants of human breast cancer cells (Fang et al., 1992; Wellstein et al., 1992) and defined a signaling pathway of this protein (Souttou et al., 1997). The gene discussed is PTN; the disease is breast carcinoma.