GH1 and neoplasm: Recent studies have shown the importance of autocrine/paracrine production of hGH and hPRL during human breast carcinoma cell proliferation in vitro (Kaulsay et al, 1999; Mertani et al, 2001) and have proposed that local production of PRL in vivo is more important than systemic PRL for the tumour formation (reviewed in Wennbo and Tornell, 2000).