Localization of the chromosome 22 breakpoints in two cases of acute megakaryoblastic leukemia with t(1;22)(p13;q13).

Acute megakaryoblastic leukemia with t(1;22)(p13;q13) is a rare malignancy occurring in infants and young children. The genes involved in t(1;22)(p13;q13) are unknown. In this study, dual-color fluorescence in situ hybridization (FISH) experiments with 15 probes were performed on the metaphase cells obtained from one patient to systematically narrow the region of the breakpoint on chromosome 22 and localize it to RP5-1042K10. A 22.3-kb FISH probe derived from RP5-1042K10 was used to further refine the locus of the breakpoint in this case. Southern blot analysis covering of genomic DNA from a second patient detected DNA rearrangement at a site close to the breakpoint observed with the 22.3-kb probe in the first case. A partially characterized gene, KIAA 1438, is in the vicinity of the breakpoints determined by FISH and Southern blot experiments, suggesting that this gene plays a role in this malignancy.

Lineage involvement by BCR/ABL in Ph+ lymphoblastic leukemias: chronic myelogenous leukemia presenting in lymphoid blast vs Ph+ acute lymphoblastic leukemia.

Chronic myelogenous leukemia (CML) can sometimes present in lymphoid blast phase (L-BP), and can be difficult to distinguish from Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL). Some have suggested that the determination of cell lineages involved by the Ph chromosome may be used for distinguishing CML presenting in L-BP (presumably multilineage disease) from Ph+ ALL (presumably lymphoid-restricted), although others have suggested the term 'stem cell ALL' for the multilineage process. Because it has been difficult to perform lineage studies of the Ph chromosome, we investigated the use of fluorescence in situ hybridization (FISH) with probes for BCR (on chromosome 22) and ABL (on chromosome 9) to study lineage involvement in Ph+ lymphoblastic malignancies. We analyzed routine blood and marrow specimens from eight patients who presented with Ph+ lymphoblastic leukemia and found that FISH recognized the 9;22 translocation, distinguished between the two common molecular variants, and readily identified multilineage vs lymphoblast-restricted disease. In our series, four patients had multilineage and four had lymphoblast-restricted disease. Multilineage disease was associated with morphologic features of CML at diagnosis and/or reversion to chronic phase CML after treatment leading us to consider it as CML presenting in L-BP. Patients with lymphoid-restricted disease lacked such findings. The survival of three of our four patients with multilineage disease was prolonged, at 25, 28+, and 126+ months, and when data from our entire series are added to those of 18 previously reported cases that were studied for lineage involvement (reviewed in Leukemia 1993; 7: 147), the difference in overall survival between patients with multilineage and lymphoblast-restricted disease is significant (median overall survival of 47 months vs 8 months, respectively; P=0.013, log rank). Our findings illustrate that FISH analysis can be used to recognize lineage involvement in patients presenting with Ph+ lymphoblastic malignancies, and they provide further support to the notion that multilineage and lymphoblast-restricted disease are distinct clinically as well as biologically.

Hematopathologic findings in the myeloproliferative disorders.

In the preceding paragraphs, the features that define the various members of the CMPD have been reviewed. These features are summarized in Table 4. Knowledge of these guidelines will aid the clinician and pathologist in arriving at a proper classification; however, in most cases, it is the occasional patient whose clinical, laboratory, and morphologic findings lie across the different categories that unifies these CMPDs, and that provides the challenge which makes them interesting.

Correlation between cell morphology and expression of the AML1/ETO chimeric transcript in patients with acute myeloid leukemia without the t(8;21).

The 8;21 chromosomal translocation involves the AML1 gene on chromosome 21 and the ETO gene on chromosome 8 and results in the transcription of a chimeric message. This translocation is most often associated with acute myelogenous leukemia with maturation (AML-M2). The leukemic cells of patients carrying t(8;21) often exhibit several characteristic morphologic features. We identified four cases in which the morphology led us to suspect a t(8;21), but in which this translocation was not observed by cytogenetic analysis. In two of the four cases, an AML1/ETO chimeric fragment was detected by reverse transcription and polymerase chain reaction (RT-PCR), and its sequence was found to be identical to that from patients with a cytogenetically proved t(8;21). Marrow specimens of the four patients lacking the t(8;21) cytogenetically were reviewed retrospectively with regard to seven morphologic features commonly reported to be associated with this translocation, and the results were compared to 13 morphologic controls with the t(8;21). Although none of the 13 controls had all of the characteristic morphologic features, all had at least six, as did the two t(8;21)-negative but RT-PCR-positive patients. The two patients who lacked the t(8;21) and who were RT-PCR-negative showed only three and four of these morphologic features, respectively. Both of the RT-PCR-positive patients had deletions of the long arm of chromosome 9, a common change associated with a t(8;21), supporting our assessment of these patients as having a cytogenetically undetected t(8;21).

Issues in the pathology and diagnosis of the chronic myeloproliferative disorders and the myelodysplastic syndromes.

We have attempted to discuss some of the issues that interest pathologists who are involved in the diagnosis of CMPD and MDS. In most cases, correlation of the clinical findings with the findings in the blood and marrow will allow the morphologist to arrive at a proper diagnosis. Nevertheless, there will continue to be cases that are difficult to classify, or in which the clinical features are out of keeping with the morphologic features. These cases are challenging and thought-provoking, and the application of newer diagnostic techniques, such as molecular genetics, may provide important insights.