Clinical, Cytogenetic, Immunophenotypic Characteristics and Outcome of Blastic Phase in Chronic Myeloid Leukemia: A Single Institution Experience

Chronic myeloid leukemia blastic phase (CML-BP) is the final step in the evolution of CML, and behaves aggressively, with rapid progression and short survival.

This is a retrospective study evaluating the characteristics and outcome of fifty-one patients with CML-BP who were treated in our institution between 1988 and 2013.

All patients fulfilled WHO 2008 criteria for CML-BP. The median age at diagnosis was 41 years and 54.9% were men. Of all patients, 44 (86.3%) progressed from chronic or accelerated phase, and 7 (13.7%) presented as CML-BP at diagnosis.

Using morphology and immunophenotyping, the characteristics of BP were: 70.6% myeloid (megakaryoblastic: 13.7%, myelomonocytic: 9.8%, myeloid sarcoma: 2% and promyelocytic: 2%), 23.5% lymphoid and 5.9% mixed phenotype. Thirteen patients (25.5%) had extramedullary involvement at diagnosis, of which CNS involvement was the most common (46.2%). We found major-route cytogenetic abnormalities in 23.5% (isochromosome 17 in 41.6%, trisomy 19 and double Philadelphia chromosome in 25% each).

Forty-three patients received induction chemotherapy (84.3%): 27 patients induction chemotherapy and 16 patients induction chemotherapy plus tyrosine kinase inhibitors (TKI, imatinib in 13 patients). Two patients only received TKI at diagnosis.

Results: response (2^nd chronic phase) rate was 31.4% (33.3% for myeloid BP and 69.2% for lymphoid BP, P= 0.02).

Most used chemotherapy regimens were: standard dose cytarabine plus anthracycline for myeloid BP (20 patients, 71.4%) and vincristine plus prednisone based regimens (11 patients, 91.7%) for lymphoid BP. One patient with mixed phenotype was treated with an AML based regimen and 2 patients with ALL based regimens.

Median disease free survival in patients who had response to chemotherapy with or without TKI was 4 months (1-147): 4 months for myeloid BP and 5 months for lymphoid BP (P=0.46).

Median overall survival (OS) was 4 months: 7 months for patients who responded and 2 months for non responders (P=0.04).

Only three patients received consolidation with hematopoietic stem cell transplantation, two relapsed and died in progression and one patient remains alive after a follow up of 147 months in complete remission.

There was no difference in overall survival between patients who received only induction chemotherapy from 1988 to 2000 and those who received chemotherapy and TKI from 2001 to 2013. There is a non significant tendency for worst survival in patients with major-route cytogenetic alterations at diagnosis.

Blastic phase remains a challenge in the management of CML. As far as we know there are no previous reports of characteristics and outcome of this entity in mexican population. The prognosis in this group of patients is very poor and the responses are only transitory, and allogeneic stem cell transplantation provides the best chance of a cure in CML-BP.