What is described is a method for treating cancer in a patient assaying levels of (a) CXCR1 and/or CXCR2 ligands or (b) myeloid derived suppressor cells (MDSCs) and/or neutrophils in the patient, and if the patient has increased levels of (a) or (b), then administering a therapeutically effective amount of a compound having a structure selected from the group consisting of formulas SX-517, SX-576, and SX-682