Abstract: The present invention is directed to a method of quantifying intracellular metabolite effluxes in permeabilized cancer cells for selecting cancer patients responsive for a cancer treatment, the method comprising the steps of: a) providing a sample of cancer cells taken from a patient; b) permeabilizing said cancer cells; c) incubating said permeabilized cancer cells in a reaction medium for a period of time allowing biological activity of intracellular organelles and accumulation of metabolites produced by said activity into the reaction medium in the presence of a substrate or substrates relating to a metabolite efflux or effluxes of interest, wherein said substrates used are at least glutamine and pyruvate; d) determining the quantity of metabolites relating to said metabolite efflux or effluxes of interest accumulated in the reaction medium during step c); and e) comparing the amounts of metabolites determined in step d) to equal measurements performed on control samples of the same tissue type and assessi