Multiple reports have identified the prognostic relevance of achieving an EMR at 3 and 6 months after starting TKI therapy. Marin and colleagues reported that in 282 imatinib-treated patients, there was a significant improvement in 8-year OS, progression-free survival, and cumulative incidence of CCyR and CMR in patients who had BCR-ABL1 transcripts < 9.84% IS after 3 months on treatment.25 This data highlights the importance of early molecular monitoring in order to ensure the best outcomes for patients with CP-CML.
The NCCN CML guidelines and ELN recommendations both agree that an ideal response after 3 months on a TKI is BCR-ABL1 transcripts < 10% IS, but treatment is not considered to be failing at this point if the patient marginally misses this milestone. After 6 months on treatment, an ideal response is considered BCR-ABL1 transcripts < 1%–10% IS. Ideally, patients will have BCR-ABL1 transcripts < 0.1%–1% IS by the time they complete 12 months of TKI therapy, suggesting that these patients have at least achieved a CCyR.19,23 Even after patients achieve these early milestones, frequent monitoring by RQ-PCR is required to ensure that they are maintaining their response to treatment. This will help to ensure patient compliance with treatment and will also help to identify a select subset of patients who could potentially be considered for an attempt at TKI cessation (not discussed in detail here) after a minimum of 3 years on therapy.19,26
Given the successful treatments available for patients with CML, it is crucial to identify patients with this disease, ensure they receive a complete, appropriate diagnostic workup including a bone marrow biopsy and aspiration with cytogenetic testing, and select the best therapy for each individual patient. Once on treatment, the importance of frequent monitoring cannot be overstated.