(II) BCL 2 protein is over-expressed in a proportion of AML cases. There is some evidence that this correlates with treatment response and survival and, since chemotherapy results in apoptotic cell death, this may constitute a mechanism of chemo-resistance. Retinoids down regulate BCL 2 expression AML blasts in vitro. The increased sensitivity of AML blasts to chemotherapy mentioned above, mediated by retinoid, is due to shortening of the BCL 2 half-life.