RB1 and pituitary tumor: Furthermore, crossbreeding of PTTG (-/-) mice with Rb (+/-) mice showed significant reduction in pituitary tumor development compared to PTTG (+/+)/Rb (+/-) mice; incidence of pituitary development decreased from 80% in PTTG (+/+)/Rb (+/-) animals to 30% in PTTG (-/-)/Rb (+/-) animals [27].