Ulm et al (17,18) argued that the mixed pituitary tumor originates from the steroidogenic acute regulatory protein-expressing follicular cells in the anterior pituitary, which are the primitive, pluripotent stem cells of the adult pituitary, with the capability of bidirectional differentiation of the adenohypophysis and neurohypophysis, and thus form tumors. The gene discussed is STAR; the disease is pituitary tumor.