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Mechanisms of ras mutation in myelodysplastic syndrome.

Using synthetic oligonucleotide hybridization, we have found a ras mutation in 11 of 27 patients (41%) with primary or non-therapy related myelodysplastic syndrome (MDS). This high incidence of mutation, mainly of the N-ras oncogene, was generally found in patients with disease progression to acute leukemia (8 of 11 patients = 73%). Two general mechanisms of ras mutation were found. In five patients the ras mutation was present in only a fraction of the cells; sometimes appearing in late stages of the disease, suggesting that it can occur in a differentiated cell clone. In six other patients, the ras mutation was present in the great majority of bone marrow or blood cells. The mutation was detected in mature normal lymphocytes and persisted following a complete clinical remission in two of these patients, implying that the ras mutation can occur in an early stage of cell differentiation or stem cell. Patients with a ras mutation had a median survival of nine months (all patients dead) compared to 16 patients without a ras mutation that had a median follow-up of 16 months (10 patients alive; P less than 0.005). Since 9 of the 11 patients (82%) with a ras mutation were found to have an abnormal monocytic component at diagnosis or during disease evolution, it is possible that in myeloid disorders a ras mutation is preferentially associated with myelomonocytic cell differentiation.