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for the relatively favorable outcome in this group. However, Keywords: inv(16)(p13q22); t(16;16)(p13;q22); 16 p deletions; FISH; acute myeloid leukemia; prognosis in another study, no difference in prognosis was observed between deletion and non-deletion patients. 18 To assess further the incidence of the 16 p deletions and to improve the understanding of their prognostic significance, we Introduction studied 15 patients with AML and inv(16) or t(16;16) by fluorescence in situ hybridization (FISH) using the zit14 cosmid In 1983, Arthur and Bloomfield 1,2 reported five patients with as a probe. Clinical, cytogenetic and FISH data are reported acute myeloid leukemia (AML) of myelomonocytic type (M4), here. increased marrow eosinophils and a structurally abnormal chromosome 16. Soon after, a pericentric inversion of chromosome 16, inv(16)(p13q22), was described in 18 patients Patients, materials and methods who had M4 leukemia and morphologically abnormal eosinophils with irregular, basophilic-staining granules and distinct Patients cytochemical properties. 3,4 A related chromosome abnormality, t(16;16)(p13;q22), was reported in one patient with Fifteen patients with either inv(16) or t(16;16) were diagnosed similar characteristics. 5 Further studies have suggested that at the divisions of hematology of the University Hospitals of these two abnormalities were uniquely associated with M4 Zü rich (four patients), Basel (three), Bern (three), Lausanne and abnormal eosinophils and the correlation between the (two) and of the Canton Hospitals of Sankt-Gallen (two) and karyotype and morphology has led to a subcategory in the Aarau (one) between 1992 and 1995 (Table 1). Each patient FAB classification, namely M4Eo. 6 However, both rearrangewas assigned a unique patient number for this and previous ments have been reported in other types of myeloid dispublications. [19][20][21] Additionally, 10 patients with AML (nine) or orders. 7,8 In most studies, the presence of inv(16)/t(16;16) has acute lymphoblastic leukemia (ALL) (one) and normal karyobeen associated with a high cure rate with standard chemotypes or aberrations other than inv(16) or t(16;16) were investitherapy and a relatively favorable prognosis. [9][10][11][12][13] gated by FISH and served as controls. Informed consent was Inv(16) and t(16;16) have been shown to involve, on 16p13, obtained from each patient. a smooth muscle myosin heavy chain gene (MYH11) and, onThe diagnosis and classification of patients were based on morphologic and cytochemical examination of peripheral blood (PB) films, bone marrow (BM) aspirate and biopsy speci-

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CD34/QBEND10 immunostaining has been assessed in 150 bone marrow biopsies (BMB) including 91 myelodysplastic syndromes (MDS), 16 MDS-related AML, 25 reactive BMB, and 18 cases where RA could neither be established nor ruled out. All cases were reviewed and classified according to the clinical and morphological FAB criteria. The percentage of CD34-positive (CD34 +) hematopoietic cells and the number of clusters of CD34+ cells in 10 HPF were determined. In most cases the CD34+ cell count was similar to the blast percentage determined morphologically. In RA, however, not only typical blasts but also less immature hemopoietic cells lying morphologically between blasts and promyelocytes were stained with CD34. The CD34+ cell count and cluster values were significantly higher in RA than in BMB with reactive changes (p<0.0001 for both), in RAEB than in RA (p=0.0006 and p=0.0189, respectively), in RAEBt than in RAEB (p=0.0001 and p=0.0038), and in MDS-AML than in RAEBt (p<0.0001 and p=0.0007). Presence of CD34+ cell clusters in RA correlated with increased risk of progression of the disease. We conclude that CD34 immunostaining in BMB is a useful tool for distinguishing RA from other anemias, assessing blast percentage in MDS cases, classifying them according to FAB, and following their evolution.

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Cytogenetic analysis has proven to be a mandatory part of the diagnosis of myelodysplastic syndromes (MDS) as well as a major indicator for predicting clinical course and outcome. This review concentrates on the cytogenetic classifications, the incidence and types of chromosome defects and the prognostic significance of the karyotype in adult primary MDS. Two cytogenetic classifications are currently used: one is based on the karyotype complexity (normal, single, double or complex defects), the other on clonal status (all metaphases normal, abnormal or admixture of normal and abnormal clones). Chromosome abnormalities are of both numerical and structural types. Aside from the 5q-syndrome, no specific clinico-cytogenetic entity has been reported. However, several distinct clinical and cellular features have been identified that correlate with the presence of specific chromosome defects such as inv(3)/t(3;3), +6, t(5;12), del(17p) and del(20q). The presence of complex defects is associated with reduced survival and a high risk of leukemic transformation. Among single defects, specific abnormalities may define distinct prognostic groups. Patients with del(5q) as a sole chromosome defect and a refractory anemia without excess of blasts have a favourable prognosis. For patients with trisomy 8 or monosomy 7 there may be distinct types of clinical evolution. Most patients with the 3q21q26 syndrome have a short survival. The presence of two chromosome defects may constitute an independent cytogenetic entity probably associated with relative poor prognosis. Karyotypic evolution generally represents a poor risk factor. The combination of cytogenetics with clinical and hematological features has proven to provide for a better prediction of patients' survival, leukemic transformation and response to treatment. Several scoring systems have been developed. They have to be improved by the study of new patients according to strict clinical and cytogenetic criteria and by the addition of newly recognized prognostic indicators such as histopathological features and molecular genetic mutations.

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