Efficacy of Tyrosine Kinase Inhibitors in Third Line Therapy in Chronic Phase Chronic Myeloid Leukemia

Introduction.Overall survival (OS) of patients in chronic phase (CP) chronic myeloid leukemia (CML) dramatically increased in the era of tyrosine kinase inhibitors (TKI). Meanwhile nearly half of patients discontinue 1-st line Imatinib due to resistance or intolerance. Half of them subsequently failure treatment with second line TKI. It seems that 20-25% of CP CML patients need 3-d line therapy (TKI-3l). There are a few reports regarding durable outcome of TKI-3l.

Materials and Methods. In our retrospective study 53 patients (20 male, 33 female) with CML CP treated either by Nilotinib 400 mg BID (n=18), Dasatinib 100 mg QD (n=33) or Bosutinib 500 mg QD (n=5) as TKI-3l were included. The median age at the time of diagnosis was 46 years (23-88 years). The main reason for previous TKIs discontinuation was resistance: 48/53 (91%) had failure of one and 42/53 (79%) patients had failure of both previous TKIs treatment. Median CML duration before TKI-3l was 55 months (2-314 months). Before TKI-3l mutation analysis was performed in 35 patients: 18 mutations were revealed in 16 (46%) patients including T315I mutation in 3 cases. At the moment of 3-d line TKIs therapy initiation, all patients were in CP and 43/53 (81%) had at least complete hematologic response (CHR), 8/53 (15%) patients had major cytogenetic response (MCyR) including 1 patient with complete cytogenetic response (CCyR).

Results. At the time of analysis, the median duration of TKI-3l therapy was 21 months (1-67 months). No additional patients achieved CHR, but during observational time CHR was maintained nearly in all 40/43 (93%) patients with CHR at baseline. New cases of MCyR and CCyR were observed in 15/45(33%) and 11/52(21%) of patients, respectively. Median time to MCyR and CCyR was 3.4 (3-8) and 5.2 (3-13) months, respectively. Median duration of MCyR and CCyR was 9.3 (1-43) months and 4.5 (3-6) months, respectively. Patients with resistant mutations did not obtain any cytogenetic response. TKI-3l treatment was discontinued in 21 patients. Intolerance was the reason of treatment discontinuation in 5/53(10%) cases. Progression to accelerated or blastic phases during therapy or after discontinuation occurred in 8/53 (15%) patients. Median time to progression was 14.7 months (1-46 months). There were 13 deaths in overall group of 53 patients. Two-year OS in TKI-3l was 67%. All patients with MCyR were alive and preserved CP phase.

Concluson: Our results showed that 20% of patients might obtain at least CCyR and benefit with TKIs as third line. Therefore, after two TKI lines patients, who are not eligible for allogeneic transplantation and without resistant mutations should be treated with one more line of TKI therapy.