A method of selectively treating a subject having cancer, comprises selectively administering a therapeutically effective amount of (S)-Pyrrolidine-1,2-dicarboxylic acid 2-amide 1-({ 4-methyl-5-[2-(2,2,2-trifluoro-1,1-dimethyl-ethyl)-pyridin-4-yI]-thiazol-2-yl} amide) or a pharmaceutically acceptable salt thereof, to the subject on the basis of the subject having a glutamine at position 859 of the catalytic p110-alpha subunit of PI3K. The method can includes assaying a biological sample from the subject for the presence or absence of a glutamine at position assaying a biological sample from the subject for the presence or absence of a glutamine at position 859 of the catalytic p110-alpha subunit of PI3K. Also disclosed is a method of genotyping an individual comprising detecting a genetic variant that results in an amino acid variant at position 859 of the encoded catalytic p110-alpha subunit of PI3K.
