Monitoring MRD. (A) MRD by multiparameter flow cytometry (MFC) for patients with classic hairy cell leukemia (n = 31). Testing on the first 3 time points was done on BM specimens and the rest on peripheral blood. (B) MRD by IgH PCR for patients with classic hairy cell leukemia (n = 31; testing not done for all patients at diagnosis). The results for MFC and PCR at various time points do not always belong to the same patients because of sample inadequacy or lack of testing. MRD evaluations for patients with HCLv were not included in these figures.