PRL and neoplasm: Compared with the DRD2−/− mice, the plasma PRL levels in the peripheral blood (Fig. 3a, P < 0.01) and PRL mRNA expression levels in the pituitary gland (Fig. 3b, P < 0.05) were decreased, and the tumor/body weight ratio (Fig. 3c, P < 0.001) was decreased significantly in the DRD2−/−MAPK14+/− mice.