Sudden Blastic Transformation (SBT) in Patients (pts) with Chronic Myeloid Leukemia (CML) Treated with Imatinib Mesylate.

Imatinib has become standard therapy for pts with CML in chronic phase (CP). SBT has been reported in pts receiving IFN-α, at a rate of 0.5% to 2.5% during the first 3 years of therapy. There is little information on the occurrence of SBT among pts treated with imatinib. Here we report 3 pts who developed SBT, defined as occurring after being found in complete cytogenetic remission (CG CR). These 3 pts represent 0.5% of 557 pts who received imatinib at MD Anderson for chronic phase CML. The total population has been followed for a median of 33 months (range, 1 to 56). Pt #1 was a 54 yr old female with a variant Ph translocation, t(9;22;19;10) (q34;q11.2;p13.1;q22). Sokal risk was low. She started imatinib 400mg/day within 4 mos from diagnosis, achieved a CG CR within 3 mos and was still in CG CR after 9 mos with BCR-ABL/ABL 0.66%. On routine follow-up at 12 mos she was found in myeloid blast phase with 48,XX,+8,t(8;21)(q22;q22),t(9;22;19;10) (q34;q11.2;p13.1;q22), +der(22)t(9;22;19;10) in all 20 metaphases. She received standard induction chemotherapy followed by bone marrow transplantation and is alive and in CR after 24+ months. Pt #2 was a 51 yr old female initially treated with IFN-α. She achieved a CG CR but discontinued therapy because of toxicity after 18 mos. Fourteen mos after stopping IFN-α she had a CG recurrence (35% Ph-positive) and was started on imatinib 400mg/day. Three mos later she was in CG CR and BCR-ABL was undetectable by nested PCR; a similar result was found after 9 mos of therapy. 9 mos later (18 mos after start of imatinib) she had a lymphoid SBT (precursor B-cell). CG showed 45,XX,-8, t(9;22) (q34;q11.2), −20,+mar in one metaphase, and 11 metaphases were diploid. No ABL mutations were identified. She achieved CR with HCVAD + imatinib and is currently receiving a BMT. Patient #3 was a 27 yr old pt who received imatinib 800 mg/d as first line of therapy for CML in CP with intermediate Sokal risk score. Three mos after start of therapy he was in CG CR and repeated analyses showed continued CG CR up to mo 15, with the lowest BCR-ABL/ABL 0.12 at mo 6. On mo 18 he had a lymphoid SBT (precursor B phenotype) with 43–46,XY, −7, −8,i(9)(q10),t(9;22)(q34;q11.2), −13, −17, −21,+der(22)t(9;22),+mar in 13 metaphases and one diploid metaphase. No ABL mutations were identified. He was treated with HCVAD + imatinib and achieve a CR, becoming undetectable for BCR-ABL by nested PCR. He is undergoing a BMT. In pts 2 and 3, transformation was associated with a sudden drop in platelet counts. These isolated events should alert the physicians to continued monitoring of pts on imatinib and consider marrow studies in the event of late, unexpected peripheral blood count changes. Still, SBT is rare, probably less common that seen with IFN-α therapy.