In addition, use of the Cre-LoxP system to knockout Rb in the mouse pituitary proopiomelanocortin (POMC) cell lineages (corticotrophs and melanotrophs), together with expression of firefly luciferase under the control of the POMC promoter has generated a model allowing real time imaging of tumour growth, using bioluminescence, which allows accurate evaluation of the efficacy novel therapies including the chemotherapeutic action of doxorubicin (Vooijs et al., 2002). Here, RB1 is linked to neoplasm.