The BRAF V600E mutation in hairy cell leukemia and other mature B-cell neoplasms

The somatically acquired V600E mutation of the BRAF gene has been recently described as a molecular marker of hairy cell leukemia (HCL). We developed an allele-specific PCR for this mutation, and studied 62 patients with HCL, one with HCL variant, 91 with splenic marginal zone lymphoma, 29 with Waldenström macroglobulinemia, and 57 with B-cell chronic lymphoproliferative disorders. The BRAF V600E mutation was detected in all HCL cases, and in only two of the remaining 178 patients. These two subjects had a B-cell chronic lymphoproliferative disorders that did not fulfill the diagnostic criteria for HCL. Despite the PCR positivity, the mutation could not be detected by Sanger sequencing in these two cases, suggesting that it was associated with a small subclone. We conclude that the BRAF V600E mutation is present in all HCL patients and that, in combination with clinical and morphological features, represents a reliable molecular marker for this condition.