THE SIGNIFICANCE OF MINIMAL RESIDUAL DISEASE IN HAIRY-CELL LEUKEMIA TREATED WITH DEOXYCOFORMYCIN - A LONG-TERM FOLLOW-UP-STUDY

We investigated the clinical significance and long-term follow-up of d etecting minimal residual disease (MRD) in hairy cell leukaemia (HCL) in complete remission (CR) after treatment with deoxycoformycin (DCF). MRD was assessed in 23 patients by immunophenotyping peripheral blood and bone marrow frozen sections using a panel of antibodies, CD11c, C D25, CD103 and HC2, which detect hairy cells. 31 cases with active HCL were used as controls. 10/23 patients (43%) had MRD in bone marrow (s even), blood (one) or both sites (two) which was not detected on haema toxylin-eosin bone marrow sections nor by immunohistochemistry on para ffin sections in six cases tested, Sequential studies in four cases di d not show changes in the amount of MRD. At a median follow-up of 72 m onths (range 15-108), 5/23 (22%) patients have relapsed with a median time of 59 months (range 15-105). MRD was detected in three of the fiv e patients who relapsed. In the two patients with negative MRD, one re lapsed with an abdominal mass and the other was a late relapse at 84 m onths. MRD was also documented in 7/18 patients who continued in clini cal CR for a median of 80 months (range 63-98). There were no statisti cal differences in disease-free survival between MRD+ and MRD- patient s (P = 0.8). Our findings indicate that relapse after long-term remiss ion achieved with DCF cannot be predicted when MRD is detected by sens itive methods. A search for other parameters such as proliferative rat e of the residual cells or chest and abdominal CT scan might identify patients with a higher probability of disease recurrence.