Patients and analysis of leukaemic cells Data of newly diagnosed de novo AML patients at our six institutions from 1994 to 1999 were studied. At one institution, data were available only for 1997–99. Cases meeting the criteria of biphenotypic leukaemia (Catovsky et al, 1991) were excluded.
Immunophenotyping was carried out using two-colour flow cytometry (FCM), or, since 1997, by three-colour FCM using a CD45 gating method (Miyazaki et al, 1996). The antibodies used were directed against CD2, CD5, CD7 (clone M-T701), CD10, CD20, CD33, CD56 (Pharmingen, San Diego, CA), CD3, CD4, CD8, CD13, CD14, CD16, CD19, CD34, CD45, HLA-DR (Becton Dickinson, Mountain View, CA), and CD41a (Coulter, Hialeah, FL). Lymphocytes in the samples were recognized by their antigen profile, scatter properties and bright positivity for CD45. Only data free of lymphocyte contamination were accepted. CD7 was regarded as positive when at least 20% of gated cells were more fluorescent than the isotype-matched negative control.
Karyotypes were interpreted using the standard criteria [International System for Human Cytogentetic Nomenclature (ISCN, 1995)]. An abnormal clone was defined as more than two metaphases with an identical chromosomal aberration. Normal karyotype was defined as no clonal abnormalities in 20 examined metaphases. Data with insufficient metaphases were excluded. The prognostic cytogenetic categories were defined based on previous reports (Keating et al, 1988; Dastugue et al, 1995; Grimwade et al, 1998; Slovak et al, 2000). That is, ‘favourable’ was inv(16), t(15;17) and t(8;21); ‘unfavourable’ was −5, −7, 5q–, 7q–, t(9;22), abnormalities of chromosomes 3q and/or 11q and a complex karyotype (more than three chromosomal abnormalities); and ‘intermediate’ was all other karyotypes. Because the prognosis was favourable in our cases who had both favourable and unfavourable chromosomal aberrations, such cases were included in the ‘favourable’ category.
Successfully analysed data for both the phenotype and cytogenetics were available for 256 cases (89% of all de novo AML cases in our institutions during the study period). The data for 237 of the 256 cases were obtained by analysis of marrow cells. Among the 256 cases, four cases with intermediate cytogenetics (one was CD7+) and two cases with unfavourable cytogenetics (one was CD7+) died before receiving chemotherapy. The chemotherapeutic regimens were similar in the six institutions. For acute promyelocytic leukaemia, all-trans retinoic acid was used for remission induction.