Nilotinib in Chronic Myeloid Leukemia Patients in Chronic Phase (CMLCP) with Imatinib Resistance or Intolerance: 2-Year Follow-up Results of a Phase 2 Study.

Background: Nilotinib is a potent and highly selective BCR-ABL kinase inhibitor approved for the treatment of Philadelphia chromosome-positive chronic myeloid leukemia patients in chronic (CML-CP) or accelerated phase (CML-AP) who are resistant or intolerant to prior therapy including imatinib.

Methods: This open-label, single-arm, phase 2 study was designed to evaluate the efficacy and safety of nilotinib in CML-CP patients resistant or intolerant to imatinib. Imatinib intolerant patients with prior major cytogenetic response (MCyR) on imatinib were not eligible for this trial. Nilotinib was dosed at 400 mg twice daily with the option of dose escalation to 600 mg twice daily if responses were inadequate. Rate of MCyR was the primary endpoint. Secondary endpoints included complete cytogenetic response (CCyR), complete hematological response (CHR), duration of MCyR, survival, and safety.

Results: A total of 321 CML-CP patients (71% imatinib-resistant; 29% imatinib-intolerant) were evaluated. Most patients were heavily pretreated with 72% having received more than 600 mg/day of imatinib prior to study entry. Furthermore, imatinib-intolerant patients could not have achieved prior MCyR on imatinib therapy. Median duration of prior imatinib treatment was 33 months (range 0.3–95 months). Dose reductions (25%) and discontinuations (15%) due to adverse events were infrequent on nilotinib therapy and median dose intensity (788 mg/day; range 151–1112 mg/day) closely approximated the planned dose. Median duration of exposure was 465 days (15.5 months). Overall, nilotinib therapy resulted in rapid and durable hematologic and cytogenetic responses. Of all imatinib-resistant and –intolerant patients, 58% achieved MCyR (1 month median time to MCyR), with 72% of patients having a baseline CHR achieving MCyR. The MCyR rate was 63% in imatinibintolerant and 56% in imatinib-resistant patients, respectively. Overall, 42% of patients achieved a CCyR (50% in imatinib-intolerant and 39% in imatinib-resistant patients, respectively). Responses were durable, with 84% of patients maintaining their MCyR at 18 months. Estimated overall survival (OS) rates at 12 and 18 months were 95% and 91%, respectively. Nearly half of all patients (47%) were still receiving nilotinib at the time of cut-off for data analysis. Longer follow-up has not significantly changed the safety profile of nilotinib. The most frequently reported grade 3/4 biochemical laboratory abnormalities were elevated lipase (16%), hypophosphatemia (15%), hyperglycemia (12%), and elevated total bilirubin (7%). Overall, biochemical laboratory abnormalities were transient and clinically asymptomatic. Grade 3/4 non-hematologic adverse events were infrequent with rash, headache, and diarrhea occurring in only 2% of patients. No pleural or pericardial effusions were documented during nilotinib therapy. The most common grade 3/4 hematological laboratory abnormalities included neutropenia (30%), thrombocytopenia (28%), and anemia (10%). Overall, QTcF changes greater than 60 milliseconds from baseline were infrequent, occurring in only 8 patients (2.5%), and QTcF prolongation >500 milliseconds was uncommon (<1%), occurring in only 3 patients. Brief dose interruptions were sufficient to manage most adverse events.

Conclusions: Nilotinib is highly effective and produces rapid and durable responses in CML-CP patients who failed prior therapy including imatinib due to resistance or intolerance and is an important treatment option for this patient population. Nilotinib is well tolerated with minimal occurrence of grade 3/4 adverse events; safety profile has not changed with longer follow-up.