This invention provides a method of identifying one or more subgroups of cancer patients that are likely to benefit from treatment with a monocarboxylate transporter (MCT) protein inhibitor comprising: (a) obtaining a sample of a cancer/tumor tissue from each of said cancer patients (b) determining the expression level of stromal MCT4 protein in each of said samples of cancer/tumor tissue to obtain a first dataset and (c) using the expression level of the stromal MCT4 protein from said first dataset to classify each of said sets of one or more cancer patients as stromal MCT4-positive or stromal MCT4-negative, wherein the cancer patients classified as stromal MCT4-positive are patients that are more likely to benefit from treatment with said MCT protein inhibitor. This invention also provides related methods for treating a cancer/tumor whose stromal component expresses the MCT4 protein in a patient.
