Diagnosis and Classification of MDS

The diagnosis is essentially one of exclusion in first ruling out other disorders that can also cause peripheral blood/bone marrow dysplasia and cytopenias.

The diagnosis of MDS requires minimal descriptions described by the FAB Cooperative group.8,58,161 Five categories were described on the basis of morphological criteria. With the exception of refractory anemia with ringed sideroblasts (RARS) and chronic myelomonocytic leukemia (CMML), the principal distinction among the subgroups is the percentage of blasts in the bone marrow and peripheral blood. A diagnosis of AML required the presence of more than 30 percent blasts in the bone marrow. In recent years it has been noted that this classification system is sometimes clinically inconsistent.11,162 Major confusions therefore arise: 1. The use of 30 percent blasts in the bone marrow as the dividing line between AML and MDS is biologically inconsistent and therapeutically confusing, 2. CMML is a separate entity and is related more closely to CMPDs than to the myelodysplasia; and 3. cases with significant trilineage dysplasia but less than 5 percent blasts that have a worse prognosis similar to RAEB are not recognized in the FAB schema. Therefore, the committee of the WHO11 recommended the following proposals to clarify the discussions mentioned above: 1. Lowering the cutoff value of bone marrow blasts for the diagnosis of AML from 30 to 20 percent, and eliminating the category of refractory anemia excess blasts in transformation (RAEB-T); 2. forming a separate category of myeloid neoplasms (myeloproliferative/myelodysplastic) to contain those cases that are inherently proliferative but show dysplastic features including juvenile myelomonocytic leukemia (JMML), CMML, and atypical chronic myeloid leukemia (aCML); and 3. considering the severe multilineage dysplasia without increasing marrow blasts as a separate entity. The FAB classification and proposed WHO classification of MDS are given in Tables 14-6 and 14-7, respectively.

Predicting overall survival as well as the risk of AML transformation has been improved by the recent development of a scoring system (International Prognostic Scoring System)163 that incorporates three laboratory variables: percentage of bone marrow blasts, degree of cytopenias, and presence of chromosomal abnormalities. Advanced age and male sex also adversely affected survival. Isolated loss of the Y, 5q, or 20q chromosomes and normal karyotype were associated with a better prognosis (median survival 5.7 years), whereas abnormalities of chromo-

Table 14-6. FAB Classification of Myelodysplastic Syndromes (MDS)

Refractory anemia (RA)

Refractory anemia with ringed sideroblasts (RARS)

Refractory anemia with excess blasts (RAEB)

Chronic myelomonocytic leukemia (CMML)

Refractory anemia with excess blasts in transformation (RAEB-T)

Table 14-7. Proposed WHO Classification of Myelodysplastic Syndromes (MDS)

Refractory anemia or refractory cytopenia Without ringed sideroblasts With ringed sideroblasts Refractory cytopenia with multilineage dysplasia (RCMD) Refractory anemia with excess blasts (RAEB); RAEB-I (5-10

percent blasts); RAEB-II (11-20 percent blasts) 5q- syndrome Unclassifiable MDS

Myelodysplastic/myeloproliferative diseases Chronic myelomonocytic leukemia Atypical chronic myeloid leukemia (aCML) Juvenile myelomonocytic leukemia (JMML)

some 7 or complex cytogenetic changes with three or more abnormalities were associated with a worse prognosis (median 0.4 years). Management of MDS patients can now be based on the patient's respective prognostic subgrouping.

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