Unexpectedly high incidence of hypoplastic/aplastic foci in bone marrow biopsies of hairy cell leukemia patients in remission following 2-chlorodeoxyadenosine therapy.

Treatment with the purine analog 2-chlorodeoxyadenosine (2-CDA) achieves a complete response in close to 90% of patients with hairy cell leukemia, with approximately 75% remaining in prolonged remission. Recently, we unexpectedly noted foci of hypoplasia and aplasia in routine follow-up bone marrow biopsies of several hairy cell leukemia patients in remission with normal blood counts. Because of this finding we examined all available biopsies to assess the incidence of this phenomenon. A total of 94 biopsies in 31 patients were reviewed. Of these, 23 were prior to 2-CDA therapy and 71 (in 30 patients) were obtained 2-76 (mean 22) months following one or more courses of treatment. Nine patients had also received prior interferon and 7 (of whom 3 had also received interferon) had undergone splenectomy. Hypocellular foci were found in only 3 (13%) of the pre-therapy biopsies. Forty-seven of the 71 post-therapy biopsies (in 23 patients) (66%) had a total of 176 hypocellular foci. Of these 47 biopsies, 39 were without evidence of disease. A simultaneous complete blood count was normal in 34 of the 47 hypoplastic biopsies (72%). This suggests that these hypoplastic areas may not be representative of the entire bone marrow and that normal hematopoiesis may take place at other sites. However, since the longest follow-up is less than 7 yr, the potential long-term significance of these findings, such as progressive bone marrow aplasia or dysplasia, may still be unrecognised.