Studies in mice where allelic CBFB-MYH11 expression is activated in hematopoietic cells have established that leukemia is preceded by a preleukemic period of 4 to 6 months, and the median leukemia latency can be delayed or render incomplete penetrance by reducing the number of HSCs expressing CBFB-MYH11 (28, 46). The gene discussed is CBFB; the disease is leukemia.