The use of fluorodeoxyuridine synchronization for cytogenetic investigation of acute lymphoblastic leukemia

The role of fluorodeoxyuridine (FUdR) synchronization in cytogenetic analysis of acute lymphoblastic leukemia (ALL) was investigated using samples of bone marrow (BM) (10 patients) and peripheral blood (PB) (2 patients), prepared for chromosome analysis using both 24-hour unstimulated cultures (24-hr) and cultures synchronized with FUdR. The mitotic index (MI) in FUdR was lower than in 24-hr in 8 of 10 BM and 2 of 2 PB cultures. The quality of the metaphases was the same in both cultures. The FUdR had a lower percentage of abnormal cells than the 24-hr in the 7 BM samples with a normal/abnormal population and sufficient analyzable cells in each culture for comparison (p less than 0.05). PB FUdR cultures yielded only normal cells. We conclude that FUdR cultures are inferior to 24-hr cultures for chromosome analysis in ALL.

Philadelphia positive acute lymphoblastic leukemia in adults: age distribution, BCR breakpoint and prognostic significance

Clonal karyotype, clinical and blast cell features were established in 113 adults, aged 15-68 (mean 31.2) years with acute lymphoblastic leukemia (ALL). The karyotypes were: Philadelphia positive (Ph+), 23 cases; t(4;11), six cases; other chromosome findings (group II), 84 cases. Ph+ patients were older (mean 39.7 years) at presentation than the group II patients (mean 28.3 years) (p less than 0.0001). Ph+ was less frequent than expected in teenagers (15-20 years) (10.3%) and patients aged 21-50 years (21.8%), and more frequent in patients over 50 years old (43.8%) (p less than 0.01). Follow-up (between 0.5 and 4.5 years) was obtained for 108 patients. Age and karyotype (Ph+ versus group II) were prognostically significant for event-free (EFS) and overall survival (S) (p less than 0.001 in each instance). Ph+ patients fared worse than group II cases in all age groups, but karyotype added prognostic significance to age only when Ph+ and t(4;11) cases were combined (group I) (group I versus group II: EFS, p = 0.054; S, p = 0.043). The Ph breakpoint location M-bcr+ (nine cases) and M-bcr- (14 cases) was irrelevant to age (mean 37.7 and 41.3, respectively) and to prognosis. The findings indicate a fundamental difference between the genetics of ALL in most older and the majority of younger patients which may partly explain the increasingly poor prognosis with age.

Molecular investigation of 19p13 in standard and variant translocations: the E12 probe recognizes the 19p13 breakpoint in cases with t(1;19) and acute leukemia other than pre-B immunophenotype

The gene E2A has recently been cloned, mapped to 19p13 and shown to be rearranged in cases of pre-B acute lymphoblastic leukemia (ALL) with t(1;19) (q23;p13). Nine cases with a 19p13 breakpoint, four having a phenotype other than pre-B, have been investigated with the E12 probe to the E2A gene. Five cases had t(1;19) (q23;p13) and C-ALL with pre-B phenotype in four out of four cases tested. Two cases had t(1;19) (q21;p13), one with Null cell phenotype, t(4;11), and 'jumping translocations' and the other with acute non-lymphocytic leukemia M5 following bone marrow transplantation for C-ALL. Variant translocations in patients with ALL were t(15;19) (q15;p13) and t(17;19) (q21;p13). Southern blotting with E12 showed rearrangement in the cases with t(1;19) (q23;p13) and t(1;19) (q21;p13), but not in other cases with variant 19p13 breakpoints. Thus rearrangement of the E2A gene is not restricted to cases with pre-B ALL but may also occur in acute leukemias with other immunological phenotypes. Failure to detect rearrangement in 19p13 variants may be due to an E2A breakpoint outside the E12 recognition region. Alternatively, there may be further genes in this location with relevance to leukemogenesis.

First intron and M-bcr breakpoints are restricted to the lymphoid lineage in Philadelphia positive acute lymphoblastic leukemia

Knowledge of the level of commitment of the target cell in hematological malignancies may have important therapeutic and prognostic implications. Cell lineage involvement was investigated in two cases presenting with acute lymphoblastic leukemia diagnosed on clinical and immunological findings and having the Philadelphia translocation t(9;22)(q34;q11). DNA from cells separated into mononuclear (lymphoid) and granulocytic fractions was hybridized with Philadelphia breakpoint-specific probes. This revealed that the breakpoint giving rise to the Philadelphia chromosome in case 1 was within the major breakpoint cluster region and in case 2 was in the first intron of the BCR gene. Rearrangement was found in the lymphoid but not the granulocyte fraction in each case. It is therefore concluded that the target cell for chromosomal change in these cases was a lymphoid committed progenitor cell, irrespective of breakpoint location.

Trisomy 8 in acute lymphoblastic leukemia (ALL): a case report and update of the literature

A case of acute lymphoblastic leukemia (ALL) cytogenetically characterized by trisomy 8 as a sole aberration is described. The patient, one of 116 adults with ALL investigated cytogenetically, was a 36-year-old male with leukocyte count 12.3 x 10(9)/liter with 90% blasts of FAB type L1 and common ALL immunological phenotype. Remission was achieved with the current U.K. treatment trial. The patient recovered from an autologous bone marrow transplant (BMT) in first remission but relapsed 15 months later. BMT, in second remission, from an unrelated donor, was rejected. Autologous reinfusion failed and he died 26 months after diagnosis. Molecular investigation of immunoglobulin gene rearrangement identified the same B cell clone at diagnosis and in relapse. The clinical and cytogenetic findings of six published cases of ALL with trisomy 8 have been reviewed with updates supplied by the authors. These reveal an heterogeneous group of patients ranging in age from 9 months to 39 years with no apparent association with a particular immunophenotype. Four patients were alive after 10-108 months follow-up. Two patients died, in relapse, 7 and 17 months after diagnosis. Thus trisomy 8 occurs in ALL with an incidence of 1-2%. The prognostic significance of this remains to be determined.

Prognostic and biological importance of chromosome findings in acute lymphoblastic leukemia

At least 25 structural chromosomal abnormalities are now found in acute lymphoblastic leukemia (ALL). Many of the abnormalities are associated with particular clinical or blast cell features. Chromosomal translocation breakpoints in ALL are among those that define regions of the genome of oncogenic potential, the recognition of which has led to an improved understanding of the mechanisms of leukemogenesis. The prognostic importance of chromosome findings in ALL concerns demonstration of long-term survival in patients with high hyperdiploid leukemic clones and identification of patients with certain translocations who are at high risk of treatment failure and for whom alternative therapy such as bone marrow transplantation may be desirable. This review summarizes the more recent chromosomal findings in childhood and adult ALL and discusses how increasing recognition of structural change and adoption of alternative therapy for high-risk chromosomal groups may change the prognostic role of cytogenetics in this type of leukemia.

Demonstration of acquired hemizygosity and clonality in acute lymphoblastic leukemia with chromosome 7 abnormalities using hypervariable DNA probes

Clonal abnormalities of chromosome(s) 7 were investigated in two patients with acute lymphoblastic leukemia. The abnormal karyotypes were 46,XY,-7,del(6)(q13q21), + i(7q)/47,XY,del(6), + i(7q) in case 1, and 46,XX,-7,t(4;11)(q21;q23), + i(7q) in case 2. DNA from leukemic tissue was investigated with Southern blotting using hypervariable DNA probes lambda MS31 and p lambda g3 located on 7p and 7q, respectively. Restriction fragment length polymorphisms (RFLPs) were detected on the short arm in case 1 and on both arms in case 2, and a marked difference in intensity between the two alleles was observed. In case 1 the acquired hemizygosity of 7p, suggested by the cytogenetic findings, was confirmed by Southern blotting. Thus, one chromosome 7 formed the i(7q) and the other No. 7 was duplicated. In case 2 the results of the Southern blotting indicated that the size of the clone with i(7q) was considerably greater than suggested by cytogenetic analysis of the few available metaphase cells.

Possible evidence for acquired genetic activity at both chromosomal breakpoints of the Philadelphia translocation in chronic myeloid leukemia

The Philadelphia (Ph1) chromosome (22q-), found in more than 90% of patients with chronic myeloid leukemia (CML), is one part of a reciprocal translocation, t(9;22) (q34;q11), in which the oncogene c-abl moves from 9q34 to 22q11. The translocation results in the translation of an aberrant abl-related protein with tyrosine kinase activity. Genetically active genes are known to have chromatin which is hypersensitive to deoxyribonuclease I (DNase I) and to be hypomethylated. Using an in situ nick translation technique on metaphase chromosomes, we have examined DNase I sensitivity and methylation status at the breakpoints 9q34 and 22q11 in bone marrow cells from controls (two cases) and CML patients (three cases). In CML cells DNase I sensitivity was significantly increased, at both breakpoints, in the translocated chromosomes compared with their normal homologues in CML cells and with both homologues in control marrows. A hypermethylated site, seen at 22q11 in normal 22s was hypomethylated on 22q-. The 9q34 region was hypomethylated in normal and translocated chromosomes. DNase I sensitivity, seen at 22q13 in CML cells, was lost following translocation in one of three cases. This technique demonstrates alterations in chromatin conformation and methylation status at translocation breakpoints which may be related to acquired genetic activity at one or both of these sites.

Leukemia characterized by multiple sub-clones with unbalanced translocations involving different telomeric segments: case report and review of the literature

A 68-year-old man presented with t(4;11)(q21;q23), B-lineage acute lymphoblastic leukemia (ALL) which was negative for C-ALL antigen and TdT. Clonal evolution to five different, but related karyotypes, in which chromosomal material distal either to 1q11 or 1q21 was translocated to the terminal regions of 4q-, 11q, 16q, and 19p resulted in partial or total trisomy of 1q. The patient, having achieved a short remission, died 14 weeks after diagnosis. Five reports of jumping translocations in hematological malignancies, four with B-lineage malignancy, are reviewed. One (four cases) or both (one case) of the same 1q breakpoints were consistently found and 11q and 16q were repeatedly involved. Such cases, having multiple subclones with trisomy 1q, may form a distinct subgroup of ALL.

Cytogenetic studies of 21 patients with acute lymphoblastic leukemia in relapse

Karyotypes of 21 patients, originally entered into the Third International Workshop on Chromosomes in Leukemia (3IWCL), were investigated in first, second and/or subsequent relapses. Karyotypes at diagnosis were related to the relapses in the following ways: normal to normal (N-N) (five cases); abnormal to normal (A-N) (two cases); abnormal to abnormal with no change (A-A) (five cases); abnormal to abnormal with clonal evolution (A-A+) (eight cases); and normal to abnormal (N-A) (one case). The A-A group comprised two each of t(4;11) and t(9;22) cases and one pseudodiploid case; included in this group were the only two patients who did not receive intensive treatment. Both A-N cases had been pseudodiploid at diagnosis. Clonal evolution A-A+ occurred in patients who had had 47-49 chromosomes or pseudodiploidy at diagnosis and was mainly due to the addition of structural change. The additional abnormalities were different in each case. The only de novo appearance of a clone (N-A) was in host cells in relapse following bone marrow transplantation. Clonal evolution occurred in patients who had been intensively treated and who relapsed late; the median time from diagnosis to relapse studied for the A-A group was 6 months and for the A-A+ group was 24 months. Survival following relapse was shorter for patients who had had a clonal abnormality at any time (median 10 months) than for those with no abnormality at diagnosis or in relapse (median 26 months).

Six-year follow-up of the clinical significance of karyotype in acute lymphoblastic leukemia

To evaluate the importance of pretreatment karyotype in predicting long-term outcome in acute lymphoblastic leukemia (ALL), we performed a follow-up study of the 329 patients from the Third International Workshop on Chromosomes in Leukemia. Living patients have now been followed a minimum of 6 years. Patients were divided into ten groups according to pretreatment karyotype: no abnormalities, one of the following structural abnormalities [the Philadelphia chromosome, rearrangements involving 8q24, t(4;11), 14q+, 6q-] or, in the remaining cases, modal number (less than 46, 46, 47-50, greater than 50). As previously reported for achievement and duration of complete remission, and overall survival, disease-free survival differed significantly (p less than 0.001) among chromosome groups for both adults and children. Among children, karyotype was an independent prognostic factor for predicting disease-free survival. Because of the long follow-up, we now have been able to utilize statistical models to estimate the percentage of patients cured, according to karyotype alone and combined with other risk factors. Adults with the highest likelihood of cure (21-33%) were those patients with FAB-L1, a leukocyte count of 50,000/microliters or less, and one of the following chromosome groups: greater than 50, 47-50, 6q-, or normal. In children these same characteristics were associated with the highest percentage of cure (58-71% cured). In addition, we identified several groups of children with less than 15% chance of cure who clearly need to be treated as high-risk patients at diagnosis. Future studies of patients who have received risk-adapted therapy based on these chromosome data are needed to determine if more intensive treatment will improve the outlook of patients with cytogenetically unfavorable types of ALL.

Chromosomes and other prognostic factors in acute lymphoblastic leukaemia: a long-term follow-up

Cytogenetic, clinical and laboratory features at diagnosis were examined in a group of 80 children with acute lymphoblastic leukaemia (ALL) who had been followed up for a minimum of 5 1/2 years. The 17 (21%) with high hyperdiploidy tended to have low leucocyte counts and common ALL, but their favourable outcome (75% event-free survival) was independent of these factors. No patient with hypodiploidy survives while the pseudodiploid and normal groups have an intermediate prognosis. Cytogenetic analysis showed examples of patients with the well-recognized translocations and a number with apparently unique ones. Among the latter were some long-term survivors. We conclude that cytogenetic analysis identifies a good risk group of patients who remain well on long-term follow-up, but that the presence of a translocation does not necessarily imply a poor outcome.

Isochromosome 9q in acute lymphoblastic leukemia: a new non-random finding

The presence of an isochromosome is commonly associated with late-stage disease and has rarely been reported at diagnosis in hematological malignancies. Five patients (two males and three females aged 3, 6, 13, 13, and 35 years) with an acquired i(9q) at diagnosis of acute lymphoblastic leukemia (ALL) are presented; in one case it was the sole karyotypic change. The patients presented in November or January, two in 1983/84, three in 1987/88. The latter were three of 100 unselected ALL cases referred over a three year period for cytogenetics and successfully karyotyped. Two had a prior history of pancytopenia. Features of high risk ALL in these patients included age over 10 years (three cases), leukocyte counts greater than 200 x 10(9)/liter (two cases) and pre-B immunological phenotype (two cases). All achieved remission on standard protocols. One patient is disease free over 4.5 years from diagnosis. One relapsed at 3.5 years and is well following a bone marrow transplant in second remission. Follow-up for the remaining three patients is between 9 and 11 months. Our findings indicate that i(9q) frequently with additional chromosome change is a feature of newly diagnosed ALL.

Chromosome 22 breakpoints in variant Philadelphia translocations and Philadelphia-negative chronic myeloid leukemia

The standard t(9;22)(q34;q11) found in Philadelphia (Ph) chromosome positive chronic myeloid leukemia (CML) involves a highly restricted (5.8 kb) chromosome 22 breakpoint cluster region (bcr), which results in the formation of a chimeric gene comprising exons from the 5' end of bcr and protooncogene c-abl coding sequences from chromosome 9. In a survey of 21 patients with hematologic and clinical features of CML we detected rearrangement of the chromosome 22 bcr by gene probe analysis in all cases, including 16 with a standard t(9;22), two with variant Ph translocations [t(10;22)(q26;q11);t(11;22)(p15;q11)], one with a complex Ph translocation [t(9;11;22)(q34;q13;q11)], one with a complex translocation and a masked Ph[t(9;14;22) (q34;q24;q11)], and one Ph-negative case with a t(1;9)(p32;q34). These observations further substantiate the suggestion that, despite karyotypic heterogeneity, a common underlying molecular lesion, the bcr-abl gene chimera, is involved in the disease pathogenesis of CML.

Clonal evolution in Ph-negative, bcr-positive chronic myeloid leukaemia before and after bone marrow transplantation

A 26-year-old man, who presented with bilateral fundal haemorrhages, was found to have chronic myeloid leukaemia (CML). The Ph chromosome was not present but a clone with t(1;9) (p32;q34) was detected. On referral for bone marrow transplant (BMT) he was found to be in accelerated phase with clonal evolution in three cell lines inv(3)(q21q26); inv(3)(q),i(17q); inv(3q)+8. Molecular investigation revealed a breakpoint on chromosome 22 within the breakpoint cluster region (bcr) similar to that found in Ph+ cases. After BMT, from an HLA-identical sister, successful engraftment (46,XX) was accompanied by evidence of a residual host cell population with further evolution (del(7)(q22)) and persistence of the bcr+ clone. Acute myeloid leukaemia, detected 5 months later, was associated with predominance of the clone 46XY,t(1;9),inv(3q),del(7)(q22) which failed to respond to treatment and the patient died 6.5 months after BMT. This case indicates that BMT, after the acquisition of additional chromosomal change in accelerated phase, may fail owing to persistence of the leukaemic clone. In addition the BMT conditioning regimen may produce further abnormalities which confer drug resistance on the persisting clone, which can emerge as an intractable myeloid blast crisis.

Variable Philadelphia breakpoints and potential lineage restriction of bcr rearrangement in acute lymphoblastic leukemia

Philadelphia (Ph1) chromosome breakpoints in acute lymphoblastic leukemia (ALL) are of two kinds: those within the breakpoint cluster region (bcr+), as in chronic myeloid leukemia (CML), and those outside it (bcr-). These encode different c-abl messenger RNAs (mRNAs), p210 and p190, respectively. It has been suggested that one class of Ph+ ALL (bcr+) may be a variant of CML arising in a multipotent stem cell, the other (bcr-) de novo ALL initiated in a lymphoid-committed progenitor. Thirty-two cases of ALL (12 Ph1+, ten chromosomally normal, and ten non-mitotic cases) were investigated for bcr involvement. Breakpoints were found within five Ph1+ and in one normal case. There was no difference in clinical features, common ALL antigen (CALLA) positivity, cytogenetics, or response to treatment between the 6 bcr+ and 7 Ph1+ bcr- patients. Myeloid antigen expression was found in 2 bcr+ cases. Bcr rearrangement appeared to be restricted to the lymphoblastic component of marrow or blood in at least four bcr+ cases. In one case, separated myeloid and lymphoid cell fractions were both bcr+. Potential heterogeneity of the Ph1+ target cell, as seen in this study, may be more important in determining disease outcome than the precise location of the Ph breakpoint.

Differentiation induction in myelodysplasia and acute myeloid leukaemia: use of synergistic drug combinations

DNA synthesis inhibitors and vincristine greatly enhance the response of leukaemic and dysplastic cells to differentiation inducing agents such as retinoic acid (RET). Differentiation induction therapy is an attractive therapeutic approach in myelodysplasia (MDS) and in acute myeloid leukaemia (AML) in the elderly, since it should be possible to increase the production of mature cells, at the expense of precursor cells, without incurring the complications of intensive cytotoxic therapy. Single agent differentiation therapy has, however, not been highly successful. We have therefore investigated the use of synergistic combinations of agents. We treated nine patients (6 with MDS, 3 with AML) with 13-cis-retinoic acid (up to 100 mg/m2/day) in combination with either 6-thioguanine (20-40 mg/day in 14-57 day courses) or with vincristine (1-2 mg as a single injection during a four-day course of RET). Seven patients responded with an increase in the mature cells of at least one haemopoietic lineage. A concomitant decrease in marrow blasts was observed in 3/4 responding patients. The retention of dysplastic and karyotypic abnormalities and lack of a hypoplastic phase all suggested that differentiation induction was occurring in vivo. Prior failure to respond to therapy with single agents (RET in two and cytosine arabinoside in five patients) suggests that the synergy observed in vitro operates in vivo. In-vitro studies on marrow cells from seven patients demonstrated synergistic differentiation induction in 6/7 samples. The seventh patient was one of the two who did not respond clinically. The second of these clinically unresponsive patients had cells which were relatively refractory to RET in vitro, suggesting that in-vivo and in-vitro responses may be related.

Detection of the chromosomally abnormal clone in acute lymphoblastic leukemia

Bone marrow and peripheral blood from 121 children with acute lymphoblastic leukemia spent 3 hours in transit before being cultured. Cultures were harvested directly, after 24, 48, or 72 hours, and following methotrexate synchronization. Details of techniques are given. Analyzable mitoses were obtained in 78 cases. Failures contained no detectable clone and fewer than five mitoses (27 cases) or fewer than five analyzable mitoses (16 cases). A clone was found in 44 cases. In some cases the clone was found in two or more cultures, conversely a clone in the direct harvest was not always found after overnight culture and vice versa. Hyperdiploid clones were always found in the bone marrow and frequently in two or more cultures. Pseudodiploid clones found in the blood in four cases evaded detection in the bone marrow. The use of methotrexate did not yield prometaphase chromosomes or improve the yield of analyzable cells. The number of cultures employed influenced the yield of metaphases and appeared to influence clone detection. More cultures were needed to detect a pseudodiploid clone than to detect a hyperdiploid clone. Detection of a clone may be maximized by using the following combination of cultures: bone marrow direct and overnight, and peripheral blood overnight.

The (4;11) translocation in acute leukaemia of childhood: the importance of additional chromosomal aberrations

Case reports of four girls and one boy with acute lymphoblastic leukaemia (ALL) or acute myeloid leukaemia (AML) and t(4;11) are presented. The incidence of t(4;11) ascertained at diagnosis in ALL was 2.6% and in AML 5.3%. Four of the children were under 2 years and one was 11 years at diagnosis. Leucocyte counts above 71 X 10(9)/l and liver, spleen and node enlargement were found in all cases. Blasts of the four cases tested at diagnosis were negative to the c-ALL antigen and either TdT+ (ALL) or TdT- (AML M1). Maximum survival was less than 8 months. Additional chromosomal change was found at diagnosis in two cases and in relapse in a third. In the case of AML t(4;11) (q21;p15) was present as a second translocation. Additional numerical changes, in these and other reported cases, included + 6, commonly found in ALL, +8, +19, more often reported in AML. It is suggested that additional chromosomal changes in these cases support cytochemical and surface marker evidence that t(4;11) has a pluripotent target cell, similar to that of the Philadelphia translocation.

Acute lymphoblastic leukaemia with t(4;11) follows neuroblastoma: a late effect of treatment?

The case presented is of a 7-year-old girl who developed acute lymphoblastic leukaemia (ALL) with t(4;11)(q21;q23) 5 years after the onset of neuroblastoma and 4 months after completing treatment for a first relapse. Consideration is given to the relative importance in this case of genetic factors and chemotherapeutic drugs in the etiology of ALL.

The prognostic implications of chromosomal findings in acute lymphoblastic leukemia

The clinical importance of chromosome studies of leukemic tissue at diagnosis of acute lymphoblastic leukemia lies in the relationship between different chromosomal findings and prognoses. First demonstrated in 1978 [1], this relationship has been confirmed in a number of subsequent reports [2-9]. The independence of chromosomal findings from other prognostic features in predicting long-term response to treatment is now established [2-5, 7-9]. In children, a good or bad prognosis can be predicted only when a chromosomally abnormal cell line is identified. Differential prognosis, then, depends on the nature of the abnormality. In adults, as in children, the kind of abnormal clone, when present, is of some value prognostically. In addition, however, unlike the situation in children, the best prognosis in adults is associated with the chromosomally normal group.

Cytogenetics of acute lymphoblastic leukaemia in children as a factor in the prediction of long-term survival

A chromosomal classification of 93 children with acute lymphoblastic leukaemia (ALL) is presented. The chromosomal categories were normal, hyperdiploid, pseudodiploid and hypodiploid: the chromosomally abnormal cases were classified according to the presence of an abnormal clone. The longest follow-up was 9 years. Infants and older children were over-represented in the pseudodiploid category: this association was statistically significant. Patients in the hyperdiploid and hypodiploid categories had the longest first remissions and overall survival and those in the pseudodiploid category the shortest. These effects were statistically significant even when the effect of age and leucocyte count were taken into account. Thus chromosomal findings at diagnosis in ALL can be used as an independent prognostic factor.

Bone marrow chromosomes in acute lymphoblastic leukaemia: a long-term study

The bone marrow chromosomes of 25 children with acute lymphoblastic leukaemia (ALL) were examined at diagnosis before treatment, during remission, and in 12 cases, also during relapse. Follow-up was for at least six years. At diagnosis, 17 patients had a major population of chromosomally abnormal cells and of these 11 had identifiable clones. The commonest abnormality was hyperdiploidy. Eight patients had predominantly normal cells, but four of these had a minor abnormal clone. In remission, some samples were completely normal but, when pooled, remission samples had a minor population of chromosomally aberrant cells which were rarely clonal. The incidence of structural abnormalities was the same in patients who ultimately relapsed and those who remained in first remission at the end of the study, but the presence of hyperdiploid cells and/or clones in remission was more frequently associated with subsequent relapse. Relapse patterns were of two kinds: in three patients there was a return of the chromosomal abnormalities seen at diagnosis; in six others, chromosomal features in relapse were distinct from those at diagnosis. It is suggested that relapse associated with distinct chromosomal features may represent malignant transformation of a previously unaffected cell line. While chromosomal abnormalities seen prior to treatment can be related to the leukaemic event alone, abnormalities seen in remission and in relapse may result partly from drug and X-ray treatment. The relative importance of treatment and other factors to chromosomal change in ALL is discussed.

Prognostic implications of chromosomal findings in acute lymphoblastic leukaemia at diagnosis

Chromosomes were studied on diagnostic bone-marrow samples from 39 children with acute lymphoblastic leukaemia (ALL). The patients were classified, according to the chromosomal characteristics of the major proportion of their leukaemia cells, into five categories; hyperdiploid, pseudodiploid, diploid, hypodiploid, and mixed. Patients in the hyperdiploid category had significantly longer first remissions than those in all other categories, and those in the pseudodiploid category had the shortest. Neither the absence of any normal cells nor the presence of detectable clones appeared to be an adverse feature. We suggest that the proportion of hyperdiploid cells, determined by conventional chromosomal staining techniques, may be used as an additional prognostic feature in childhood ALL.