Classification and diagnosis

The classification and diagnosis of MDS are achieved chiefly through the morphological examination of blood and bone marrow. The karyotype can also provide important prognostic information. At present, molecular diagnostics are not routinely employed in the diagnosis of MDS, although the application of cDNA microarray technology may come to play an important role in the future.

The French-American-British (FAB) classification of MDS was published in 1982. This classification, criticized in recent years, has in fact been enormously useful to the field. At the very least it has allowed physicians to communicate about

Proposed model for genetic progression of MDS to AML

Fig. 8.1 Scheme illustrating some of the genetic changes favoring progression of MDS to AML

Predisposition-Inherited/ acquired Gene mutation: AML1, NF-1, DNA Repair genes

Predisposition-Complex genetic traits:

Polymorphic variants in carcinogen metabolism genes, genomic instability t(11 q23)

Normal

telomere shortening

3p-

+8

11 q-

20q-

17p

3q-

-17

12q-

-18

pi 5INK4 Methylation

RAS,

FLT3,p53 Mutation

Increasing telomere shortening

Increasing genomic instability

Telomere stabilization a very heterogeneous group of disorders and allow comparisons to be made of clinical trials. Consequently it is still widely used by hematologists. In the FAB classification there are five subtypes, as determined by peripheral blood and bone marrow morphology:

• refractory anemia with ringed sideroblasts (RARS)

• refractory anemia with excess blasts (RAEB)

• refractory anemia with excess blasts in transformation (RAEB-T)

• chronic myelomonocytic leukemia (CMML).

In 1999 the World Health Organization (WHO) published a revised classification of MDS. RA and RARS are defined as conditions with dysplastic features in the erythroid lineages only. RAEB may be split into RAEBI (5-10% blasts) and RAEBII (10-20% bone marrow blasts). The new groups are refractory cytopenia with multilineage dysplasia, del(5q) syndrome, and MDS unclassifiable. The RAEB-T of the FAB classification has disappeared because of similarities to AML, and CMML is now part of a new group of myelodysplastic/my-eloproliferative diseases. In addition there is the International Prognostic Scoring System (IPSS), a risk-based classification system in which scores are given for marrow blast percentage, cytogenetic features and cytopenias (Table 8.1). Not surprisingly, the overall score correlates with median survival. All these classification systems are in use but the need now is for more basic information about the fundamental nature of MDS rather than debates about classification.

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