PLK1 target phosphorylation status and treatment of cancer with PLK1 inhibitors

A method, comprising

• determining polo-like kinase 1 (PLK1) activity in a patient with a cancer by measuring phosphorylation of a PLK1 target of a cancer sample from the patient (a) prior to a treatment of the patient with a PLK1 inhibitor and (b) after the treatment of the patient with the PLK1 inhibitor, wherein the cancer is acute myeloid leukemia (AML), the PLK1 inhibitor comprises onvansertib, and the PLK1 target is translational control tumor protein (TCTP), wherein measuring phosphorylation of the TCTP of the cancer sample from the patient after the treatment of the patient with the PLK1 inhibitor comprises measuring phosphorylation of serine 46 of TCTP from about 3 hours to 5 days after the treatment of the patient with the PLK1 inhibitor;
• selecting the patient for receiving further treatment with the PLK1 inhibitor if the phosphorylation of TCTP of the cancer sample from the patient (b) after the treatment is reduced at least 50% relative to the phosphorylation of TCTP of the cancer sample from the patient (a) prior to the treatment;
• and
• administering an effective amount of onvansertib to the selected patient, thereby treating AML in the selected patient,
• wherein the cancer sample is a blood sample.