[Myelodysplastic syndromes (MDS). Aspects of hematopathologic diagnosis]

Myelodysplastic syndromes (MDS) are a heterogenous group of clonal stem cell disorders which generally occur in older adults but may also affect children. Primary MDS should be distinguished from secondary MDS associated with antineoplastic or immunosuppressive therapy (t-MDS), exposure to toxic compounds, or genetic disorders. The establishment of a neoplastic clone is reflected by dysplastic features and impaired function which may affect all three hematopoietic cell lineages. The ineffective hematopoiesis which causes bone marrow failure is accompanied by peripheral blood cytopenia and is considered to result from increased apoptosis, at least in the less advanced MDS stages. The elucidation of the molecular pathogenesis of MDS has provided evidence that chromosomal abnormalities are present in about 50% of patients with primary MDS. They include numerical aberrations such as monosomy 5 or 7, trisomy 8, loss of the Y-chromosome and structural abnormalities such as deletion of the long arm of chromosome 5 (5q-syndrome), 7, or 8. Based on the percentage of blasts (<5%, 5-20%, 20-30%) and the presence of >15% ringed sideroblasts for marrows with <5% blasts, the French-American-British (FAB) classifies MDS into 4 morphologic categories: refractory anemia (RA), refractory anemia with excess of blasts (RAEB), refractory anemia with excess of blasts in transformation (RAEB-t), and refractory anemia with ringed sideroblasts. The fifth morphologic type is chronic myelomonocytic leukemia characterized by peripheral blood monocytosis (>1x10(9)/l). However, a modification of this classification will be proposed by the World Health Organization, with the intention of lowering the threshold for the diagnosis of AML from 30% to 20% blast cells. In patients presenting with cytopenias suggesting impaired hematopoiesis, the initial diagnosis depends mainly on the cytological evaluation of bone marrow and blood smears and the histological findings of trephine bone marrow biopsy. In a retrospective analysis we evaluated the occurrence of the distinct FAB-categories as percentage of the total number of MDS cases diagnosed at the Institute of Pathology of the University of Freiburg. A total of 63% fullfilled the criteria of RA/RARS, 17% of RAEB, 14% of RAEB-t, and 6% of CMML. A fibrotic variant of MDS was observed in 7.67% of all cases, ranging from 2.34% in RA up to 15. 42-15.84% in the categories which did not show significant differences with regard to myelofibrosis. The histologic evaluation of a trephine bone marrow biopsy is of critical importance for the evaluation of fibrotic or hypocellular MDS since these patterns are not reflected by the cytological examination. The combined cytological and histological diagnosis of bone marrow and peripheral blood is a reliable tool for the initial diagnosis of MDS. In addition, cytogenetic and molecular analysis should be performed. Presently, the risk of leukemic transformation is evaluated using the International Prognostic Scoring System for MDS, which is the sum of the scores of bone marrow blasts, karyotypes and cytopenia. In the context of clinical trials therapeutic modalities should be considerd according to the age and the general performance state and the prognostic scores of individual patients.