MTOR and plasma cell myeloma: Studies of myeloma cells have also described a similar antiproliferative effect of different concentrations of rapamycin when tested over a wide concentration range [17], and previous in vitro studies of primary human AML cells suggest that some patients show no inhibition of mTOR activity when testing rapamycin ≤20 nM and with a maximal effect being reached at rapamycin >50 nM [18].