The blasts of 10-40% of acute myeloid leukaemia (AML) patients express CD7. Debate exists over whether CD7-positivity indicates an unfavourable prognosis in de novo AML (Kita et al, 1993; Lauria et al, 1994; Kornblau et al, 1995; Venditti et al, 1998). Meanwhile, the type of cytogenetics, which can be classified into three prognostic categories, is a strong prognostic factor in AML. Kornblau et al (1995) reported that CD7 expression in AML was rare in patients with favourable cytogenetics compared with other patients. However, their study included many cases who had an antecedent haematological disorder, which often results in leukaemic cells' having unfavourable cytogenetics and expressing CD7. Further, there have been no reports of an association between CD7 expression and all three prognostic cytogenetic categories in AML. We reassessed the clinical significance of CD7 expression in association with the cytogenetics in adult de novo AML.
Debate exists over whether CD7 expression indicates an unfavourable prognosis in de novo acute myeloid leukaemia (AML). Meanwhile, the type of cytogenetics is a strong prognostic factor in AML. We analysed 256 de novo adult AML cases and found that the proportion of CD7+ cases increased stepwise from the cases with favourable cytogenetics to the cases with intermediate and unfavourable cytogenetics (3 out of 69 cases, 51 out of 140 cases and 25 out of 47 cases respectively, P < 0·0001). CD7-positivity adversely affected the survival only in the cases with unfavourable cytogenetics (P < 0·03). We recommend that CD7 expression in AML be interpreted in association with the cytogenetics.
Patients and methods
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.
Statistical analyses Differences between two groups of data were analysed by Student's t-test or the chi-square test. Correlations between the cytogenetic categories and CD7 expression were analysed by logistic regression analysis. The Kaplan–Meier curves of survival were compared using the log-rank test. Cases that underwent stem cell transplant (SCT) or who were lost to follow-up were censored at the date of SCT or the last follow-up. The prognostic value of CD7 expression was adjusted for other variables using the Cox regression model. The median follow-up for cases alive at the time of analysis was 21·2 months.
Results and discussion
Blasts from 79 of the 256 cases expressed CD7. The patient characteristics are shown in Table I. Sixty-nine, 140 and 47 cases belonged to the favourable, intermediate and unfavourable cytogenetic categories respectively. The proportion of CD7+ cases increased stepwise from the favourable cytogenetic category to the intermediate and unfavourable cytogenetic categories, with strong statistical significance (Table I, P < 0·0001).
(n = 177)
(n = 79)
|Age, years*||55 (19–88)||51 (18–75)|
|WBC × 109/l*||8·7 (0·3–582·3)||9·2 (0·7–470·5)|
|LDH, IU/l*||555 (112–9920)||719 (140–4851)|
|Sum of favourable||66||3 (4·3%)§|
|Sum of intermediate||89||51 (36·4%)§|
|del(5q) or −5||4||8|
|del(7q) or −7||5||10|
|Sum of unfavourable||22||25 (53·2%)§|
When all cases were analysed using univariate analysis, both CD7-positivity and the worse prognostic cytogenetic categories were associated with short overall survival (OS) and disease-free survival (DFS) [OS: CD7+ < CD7− (P = 0·0003), unfavourable cytogenetics < intermediate cytogenetics < favourable cytogenetics (P < 0·0001)]. Variables that have strong associations with each other (such as the cytogenetics and CD7 expression) are difficult to analyse using multivariate analysis (Hamashima, 1993). When such analysis is performed, the true prognostic value of variables is often hidden. Hence, we then analysed the prognostic value of CD7 in each cytogenetic category. CD7-positivity did not adversely affect the OS or DFS in the favourable or intermediate cytogenetic category (intermediate, Table II). However, in the unfavourable cytogenetic category, CD7-positivity adversely affected both the OS and DFS, with statistical significance (Table II). The estimated OS at 2·5 years was 0% and 18% for CD7+ and CD7− cases with unfavourable cytogenetics respectively. The results of univariate prognostic analysis of other variables in the intermediate and unfavourable cytogenetic categories are summarized in Table II. Using a Cox multivariate analysis, the prognostic value of CD7 was adjusted for other variables that might influence the prognosis (Table II). This analysis showed again that CD7-positivity had no prognostic impact in the intermediate cytogenetic category. Conversely, in the unfavourable cytogenetic category, CD7-positivity was the sole variable associated with a short OS and a variable associated with a short DFS with the smallest P-value. When M3 cases lacking t(15;17) (see Table I, legend) were excluded from the analysis, the above statistical data did not change significantly (Table II, legend). Although the age and white blood cell (WBC) count are prognostic factors when AML patients are analysed without cytogenetic categorization, these variables had no prognostic impact in the unfavourable cytogenetic category in our cohort. Further, when the age and WBC count were included in the multivariate analyses, the prognostic impact of CD7 expression was not significantly changed in the unfavourable cytogenetic category (data not shown).
|Intermediate cytogenetic category||Unfavourable cytogenetic category|
|Age 60 years||0·013 (0·016)||0·51||0·68||0·55|
|WBC 50 × 109/l||0·0012 (0·0003)||021 (0·19)||0·95||0·76|
|Serum LDH value*||0·018 (0·12)||0·034 (0·063)||0·89||0·099 (0·011)|
|FAB subtype†||0·063 (0·037)||0·17 (0·073)||0·19 (0·84)||0·71|
|Institution‡||0·025 (0·29)||0·14 (0·73)||0·86||0·81|
|CD7+||0·79 (0·19)||0·13 (0·13)||0·011 (0·028)§||0·037 (0·0090)§|
These data indicate that when studying the prognostic value of CD7 in AML, the cytogenetics status of the study population significantly skews the results. For example, if most examined cases had intermediate cytogenetics, CD7 expression had no prognostic value. This may be the main reason why the prognostic value of CD7 in AML has been contradictory. We showed that CD7+ cases with unfavourable cytogenetics had an extremely poor prognosis. Although the number of our cases with unfavourable cytogenetics was relatively small, many events occurred in these cases (35 deaths and 15 relapses), which validated our prognostic analysis. However, we hope that our findings will be confirmed in independent studies. Why is CD7 expression frequent in patients with unfavourable cytogenetics? These cytogenetics consist of heterogeneous chromosomal aberrations and genetic defects. Is there a common genetic event in this cytogenetic group that induces CD7 expression on AML cells? Does CD7 expression simply show immaturity of AML cells, which is often associated with unfavourable cytogenetics, as observed in M0 patients? Another concern is why CD7 expression is further associated with the extremely poor prognosis in this cytogenetic group. Further studies are required to answer these questions.