To test directly whether de novo imposition of Myc hypomorphism in adults might have cancer-protective effects, and what accompanying deficits or iatrogenic pathologies such induced adult Myc hypomorphism might elicit, we constructed a mouse model in which endogenous Myc expression may be acutely, systemically and reversibly hypomorphed (Supplementary Fig. 1) to a degree broadly concordant with the ~30-60% reduced levels of Myc present in tissues of Myc+/– haploinsufficient mice30 and mice in which key Myc enhancer elements have been deleted13. The gene discussed is MYC; the disease is cancer.