Lymphoid Blast Phase

Approximately one-fourth of patients entering blast phase will have a lymphoid phenotype compared to the more common presentation of a myeloid or undifferentiated blastic phase. Patients entering lymphoid phase are often younger and less often have a prior accelerated phase documented compared to patients entering myeloid blast phase. A sudden onset of blast phase is more common in patients entering lym-phoid blast phase, and in fact can occur in patients seemingly in stable chronic phase responding to therapy with interferon and/or imatinib.40 There appears to be no evidence that prior treatment with interferon selects for patients entering the lymphoid blast phase, however.

Therapy for patients in lymphoid blast phase is generally more successful than for patients with myeloid transformation, as more patients enter a second chronic phase, which is durable enough to consider a hematopoietic stem cell transplant (see below). In a review published by the MD Anderson Cancer Center, overall, 49% of patients responded to therapy.41 In this series, patients given traditional drugs used to treat acute lymphoblastic leukemia (vincristine, pred-nisone, cyclophosphamide, adriamycin) had a higher rate of return to a chronic phase compared to patients treated with high-dose ara-C or methotrexate combined with L-asparaginase (61% vs 33% and 25%, respectively). Other series, however, have demonstrated high response rates (50% +) using high-dose cytara-bine/anthracycline-based regimens.42 Median survival rates for lymphoid blast-phase patients are approximately 9 months, compared to the median 3-4 months observed in patients with myeloid blast-phase disease. As with patients with myeloid blast phase, the impact of prior treatment with imatinib on the effectiveness of subsequent chemotherapy for lymphoid blast phase is, at present, unknown.

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