Multiple measurements in the critical first months of TKI therapy can aid response prediction and therapeutic decisions. (A) Two patients with the same BCR-ABL1 value >10% IS at 3 months of imatinib, indicating a warning (ELN) or treatment failure (NCCN). A single BCR-ABL1 measurement at 3 months may be insufficient for some patients to predict response. (B-D) Additional measurements over the first 3 months may identify a trend in response. Patients with no decline over the first 3 months may be at greater risk of treatment failure.