The contribution of Auer rods to the classification and prognosis of myelodysplastic syndromes

Refractory anaemia with excess of blasts in transformation re-evaluated with the WHO criteria: identification of subgroups with different survival

One of the major changes suggested by the World Health Organization (WHO) classification with respect to the French-American-British (FAB) proposal for myelodysplastic syndromes (MDS) was to lower the bone marrow (BM) blast count from 30 to 20%, thus eliminating the refractory anaemia with excess of blasts in transformation (RAEB-t) category. However, a general consensus has not been reached, and several authors still retain RAEB-t as an MDS sub-entity. We re-evaluated our series of 74 patients classified as RAEB-t according to the FAB criteria by stratifying them into two subsets: patients with at least 5% peripheral blast (PB) cells but with BM blasts <20% (group I) and patients with BM blastosis between 20 and 30% and PBs <5% (group II). We found differences among the two groups regarding sex, haematological parameters at presentation (white blood cell and neutrophil counts, haemoglobin level) and frequency of infectious episodes during the course of disease. We did not find differences as to the frequency of acute myeloid leukaemia transformation, but a significant difference was evidenced as to survival (9.3 vs. 16 months in group I vs. group II, respectively; p = 0.02). Furthermore, at our institution, we compared the RAEB-t group I patients who, based on >5% PBs, should be included in the RAEB-II category according to the WHO criteria, with a group of 98 patients who were diagnosed as RAEB-II according to the WHO criteria. The findings showed that the aggregation of these two subsets appeared inappropriate, because patients of the two groups showed different clinical features and rates of acute transformation. In conclusion, the RAEB-t entity according to the FAB criteria, although including heterogeneous clinical patient subsets, should more likely be considered as an advanced stage of MDS, rather than a true acute myeloid leukaemia.

Classification and scoring systems in myelodysplastic syndromes: a retrospective analysis of 311 patients

The main objective of this study was to evaluate the role of the recent World Health Organization (WHO) classification for assessing prognosis in patients with myelodysplastic syndromes (MDS). To this effect, we analyzed the prognostic impact of the WHO and French-American-British (FAB) morphologic classifications and of four different scoring systems in a series of 311 patients with primary MDS diagnosed between October 1990 and June 2001. Both the FAB and WHO classifications identified groups with different prognoses (p<0.0001), those presenting refractory anemia (RA) and refractory anemia with ringed sideroblasts (RARS) showing the best prognosis. The WHO classification subdivided RA into RA with only red cell dysplasia, and refractory cytopenia with multilineage dysplasia (RCMD), and RARS into RARS plus refractory cytopenia with multilineage dysplasia and ringed sideroblast (RCMD-RS). In our population, we have shown that the two subtypes characterized by dysplasia affecting exclusively the erythroid population (RA and RARS) have a better prognosis, with a median survival of 122.2 and 81.9 months, respectively, than those with multilineage dysplasia (RCMD and RCMD-RS) with a median survival of 32.3 and 43.2 months, respectively. There were no significant differences in median survival comparing RA with RAS (p<0.95), or comparing RCMD with RSCMD (p<0.97). Besides, the four scoring systems discriminated our MDS patients in terms of survival, and an increase in prognostic capacity was achieved on adding the score to the morphological classifications. Risk scoring had a greater prognostic impact than the FAB and WHO classifications. Prognostic scoring systems may be an important tool for risk stratification in hematological practice, and add significance to morphological classification. Combined application of the WHO classification and score system is useful for improving the identification of patients with a poorer prognosis. The WHO classification establishes more homogeneous subcategories than the FAB classification and is also able to identify groups with different prognoses.

Novel therapies for myelodysplastic syndromes

BACKGROUND

The assessment of patients with myelodysplastic syndromes (MDS) and the choice of therapies remain challenging. New therapies are now emerging after the identification of molecular targets that result in improvement of hematologic parameters and may hold promise for the prevention of disease progression.

METHODS

A review of the English literature was performed that included original articles and related reviews from MEDLINE (PubMed) and abstracts based on published meeting material.

RESULTS

MDS is a heterogeneous group of disorders. Although current classification and prognostic schemes have proven valid to define subgroups, they are insufficient to take into consideration the significant biologic diversity of MDS. New molecular targets are identified as the mosaic of pathophysiologic pathways in MDS is being unraveled. Novel and targeted therapeutic agents, such as the inhibition of farnesyl transferases and receptor tyrosine kinases, more potent thalidomide analogs, and arsenic trioxide, have shown encouraging results and may offer durable benefit to patients with MDS.

CONCLUSIONS

Although progress has been made in the understanding of clinical manifestations and some of the molecular pathways underlying ineffective hematopoiesis and leukemic transformation in MDS, intensive clinical and laboratory research continues to 1) identify further relevant pathophysiologic pathways, 2) better define MDS subgroups, and 3) develop new drugs based on a clearer understanding of disease biology.

Refractory anemia with excess of blasts in transformation: analysis of reclassification according to the WHO proposals

The category of "refractory anemia with excess blasts in transformation" (RAEB-T) has been abandoned in the new WHO-classification of myelodysplastic syndromes (MDS). The majority of patients previously belonging to this category are now classified as acute myeloid leukaemia (AML). In the FAB-classification, patients had been assigned to the RAEB-T category if they had either (1) a medullary blast count between 20 and 30% or (2) a peripheral blast count of at least 5%, or (3) Auer rods detectable, irrespective of the blast count. We analyzed these subtypes of RAEB-T in terms of hematological characteristics, karyotype anomalies, and prognosis. Patients with more than 20% medullary blasts and patients with at least 5% peripheral blasts as the sole defining parameter for RAEB-T had a median survival of 6 months, as compared to 11 months in patients with Auer rods as the sole defining parameter. The presence of Auer rods therefore does not convey a particularly bad prognosis and does not justify placing patients in a high-risk category of MDS or even classifying them as AML. This finding supports the elimination of Auer rods as a parameter for classification in the new WHO system. On the other hand, the reclassification into RAEB II (according to WHO proposals) of previous RAEB-T patients with a peripheral blast count of at least 5% is problematic, because this feature predicts a median survival not different from that of AML patients.

Myelodysplastic syndromes, from French-American-British to World Health Organization: comparison of classifications on 431 unselected patients from a single institution

In 1999 a working group of the World Health Organization (WHO) published a revised classification for myelodysplastic syndromes (MDS): RA, RARS, refractory cytopenia with multilineage dysplasia (RC+Dys), RAEB I and II, del (5q) syndrome, and MDS unclassifiable. Chronic myelomonocytic leukemia (CMML) and RAEB-t were excluded. Standard French-American-British (FAB) and new WHO classifications have been compared in a series of patients (n = 431) from a single center, analyzing morphologic, clinical, and cytogenetic data. According to the WHO findings, dysgranulocytopoiesis or dysmegakaryocytopoiesis only were found in 26% of patients with less than 5% medullary blasts. These patients are thus unclassified and should remain in the subgroups RA and RARS. Splitting of heterogeneous RAEB into 2 subgroups according to blast count was supported by a trend to a statistically significant difference in the single-center study population. Patients with CMML whose white blood cell counts are above 13 000/microL may be excluded from the MDS classification, as warranted by WHO, but a redistribution of patients with dysplastic CMML according to medullary blast count leads to more heterogeneity in other WHO subgroups. Although the natural courses of RAEB-T and acute myeloid leukemia (AML) with dysplasia are different, comparable median survival durations after treatment in patients with RAEB-T and AML were in favor of the proposed 20% medullary blast threshold for AML. The homogeneity of subgroups was studied by evaluating prognostic scores. A significant shift into lower IPSS risk groups was evident in the new classification. These data cannot provide evidence for the new WHO proposal, which should not be adopted for routine clinical use at present. Some of its aspects can provide a starting point for further studies involving refined cytogenetics and clinical results.

Validation of the WHO proposals for a new classification of primary myelodysplastic syndromes: a retrospective analysis of 1600 patients

In 1982, the French-American-British (FAB) cooperative group proposed a classification of myelodysplastic syndromes (MDS) based on morphological features in blood and bone marrow, namely on medullary and peripheral blast count, Auer rods, ring sideroblasts and the number of monocytes in the peripheral blood. This classification has been used for numerous studies regarding morphology, prognosis and treatment of MDS. Some details of this morphological classification remained unclear, and some patients were unclassifiable. A working group of the World Health Organization (WHO) recently proposed a new classification of MDS, based on a significant modification of the original FAB proposals. CMML and RAEB-T were removed from the MDS classification and RAEB was split into two groups with medullary blast counts below and above 10%. In addition, a group of patients with less than 5% medullary blasts but evidence of multilineage dysplasia was defined. MDS patients with 5q- as the sole chromosomal anomaly were also considered a separate group. The aim of the present study was to validate the new classification with respect to prognostic importance, and to correlate it with cytogenetic and hematological features in a large series of patients (n=1600) with a long-term follow up. We were able to confirm a significant difference in prognosis between RAEB I and RAEB II, as well as a difference between refractory anemia and multilineage dysplasia. Furthermore, patients with 5q- anomaly had a much better prognosis than other WHO subtypes, but this was only true for patients with a medullary blast count below 5%. In summary, the WHO classification appears to define morphological subgroups that are more homogeneous with respect to prognosis than the FAB subtypes.

The myelodysplastic syndromes: towards a functional classification

The French-American-British classification of myelodysplastic syndromes (MDS) has contributed greatly to better communication and conduct of clinical trials. However, the advent of novel cytogenetic, immunological and molecular techniques in recent years warrant some alterations to this purely morphological classification. This review aims at highlighting the advances which reflect more closely the unique biological and clinical features of various subtypes of MDS. We propose a comprehensive classification of MDS, to include the newly defined categories, as well as those not included in previous classifications, such as the therapy-induced and hereditary MDS. We hope that this classification will help in focusing attention on the biological features of MDS, the understanding of which will be crucial to combat this disease.

Special cytological subtypes of acute myeloid leukaemias and myelodysplastic syndromes

The recognition of distinct cytoimmunological subsets of pre-leukaemia and overt AML has been accomplished by morphological, immunological and ultrastructural studies. In many cases, a strong association has been documented between distinctive cytological features and specific chromosome changes. The primary genetic event underlying malignant transformation was also elucidated in a number of acute leukaemias and, as a matter of fact, assessment of these biological parameters has now an established role in the diagnostic work-up and in the monitoring of residual disease. On a more general basis, biological research in MDS is gradually clarifying the fundamental pathophysiological mechanisms of altered cell growth, and differentiation and therapeutic decision making in leukaemia is becoming increasingly dependent on the precise characterization of blast cells. Further refinement of the cytoimmunological classification of acute leukaemias and MDS is warranted in order to provide the physician with an updated framework of reference for the categorization of these heterogeneous haematological disorders and to improve the reproducibility of current morphological diagnosis among different centres (Castoldi et al, 1993).