RAS mutations in patients following cytotoxic therapy for lymphoma

The occurrence of Myelodysplastic Syndrome (MDS) and Acute Myeloblastic Leukaemia (AML) following cytotoxic therapy for neoplastic disease is well recognised. RAS mutations are common in patients with MDS and AML. To determine whether these lesions are found as early markers of secondary disease, we have studied the incidence of RAS mutations in the peripheral blood of 70 patients in complete remission from lymphoma. Patients were treated by standard chemotherapy regimes and/or localised radiotherapy. Treatment had been given 6 months to 14 1/2 years previously and no patient showed any sign of residual disease. Genomic DNA from peripheral blood leukocytes was amplified in vitro at target codons of N, K and H RAS genes, and mutations detected by hybridisation with oligonucleotide probes. RAS mutations were detected in 9 subjects. One patient with an N12 valine (Val) substitution had been in complete remission from Hodgkin's disease (HD) for 9 years. DNA from this patient registered in a nude mouse tumorigenicity assay (NMT). The N12 Val mutation was not detected in the original tumour tissue from the same patient. A second patient in remission from HD showed evidence of co-existent N12 cysteine (Cys) and N13 valine (Val) substitutions which were not detected in presentation material or unaffected tissues. All patients are currently haematologically normal, indicating that clones of mutant RAS bearing cells may be detected prior to any overt sign of disease.