Bone marrow morphology during induction phase of therapy for acute myeloid leukemia (AML)

Sequential bone marrow aspirates and sections from patients with acute myeloid leukemia (AML) were examined to determine if a correlation exists between bone marrow morphology during induction phase of therapy and outcome. Of 95 patients of AML diagnosed between July 1987 and December 1991, 53 uniformly treated patients (induction therapy with cytosine arabinoside and daunorubicin) had sequential bone marrow examinations performed in the 2- to 5-week period following initiation of induction therapy. Four morphologic patterns were recognized in these 53 patients: Group I (22 patients)--hypocellularity or normal regeneration (> or = 15% cellularity and < 5% blasts) on the initial 2-week marrow followed by marrows showing normal regeneration; Group II (10 patients)--hypocellularity followed by "reactive myeloblastosis" (> or = 15% cellularity, 5% to 34% blasts, with promyelocytes = or > blasts); Group III (12 patients)--residual blasts (> or = 5% blasts with blasts >> promyelocytes) in the initial posttherapy marrow; Group IV (9 patients)--atypical patterns not fitting any of the other categories. Complete remission was achieved in all 32 patients in Groups I and II without additional induction therapy, but was achieved eventually in only 10 of 21 patients in Groups III and IV combined (p < 0.005), 15 of whom received additional induction therapy. Remission duration and actuarial survival for each group were as follows: Group I: 344/596 days; Group II: 443 days/> 660 days; Group III and IV combined: 351/311 days (p = 0.017 for actuarial survival). Seven of 21 patients in Groups III and IV had unfavorable initial morphology (MO, hypoplastic AML and AML preceded by myelodysplasia) compared to only 3 of 32 patients in Groups I and II (p = 0.039). It was thus observed that "reactive myeloblastosis" with up to 34% blasts on the third or fourth week bone marrow following an initial hypocellular marrow does not require additional induction therapy to achieve durable remissions or favorable survival. Also, residual blasts that outnumber promyelocytes, and atypical patterns of regeneration correlate with lower remission induction rates, shortened survival, and unfavorable morphology on the initial diagnostic bone marrow.