Immune Thrombocytopenia Associated to Low-Dose Alemtuzumab Therapy in Chronic Lymphocytic Leukemia: A Single Retrospective Center Experience

Abstract 4598

Immune thrombocytopenia (ITP) is a common autoimmune complication in chronic lymphocytic leukemia (CLL), occurring in up to 5% of patients. The occurrence of alemtuzumab-associated ITP have been rarely reported in CLL and it has never been reported so far as a significant event complicating alemtuzumab treatment in clinical trials. Recently, a new distinctive form of secondary ITP occurring in 6 out of 215 patients with relapsing-remitting multiple sclerosis treated with alemtuzumab in a randomized, controlled phase II trial has been reported (Cuker et al, Blood 2011).

We investigated the incidence of ITP in a cohort of 64 consecutive patients treated with low-dose alemtuzumab for relapsed/refractory CLL from 2003 to 2010. Subcutaneous alemtuzumab was administered at the dose of 10 mg three times a week, up to 18 weeks.

ITP was documented in 12/64 patients: in 3 patients (4.7%) ITP developed before alemtuzumab treatment and no relapses of the autoimmune disorder were observed during the treatment; in 9 patients (14.8%, with an incidence of 5.7 events/100 patient-year) ITP developed after alemtuzumab treatment. Median time to ITP from initial alemtuzumab exposure was 12 months (range 1–42 months). Concomitant hemolytic anemia (Evans syndrome) was observed in one patient. At ITP onset, median platelet counts were 11×10⁹/L (range 3–70) and anti-platelet antibodies (Capture P® Method, ImmucorGamma, Norcross GA, USA) were found in 7 of the 8 patients tested. No patients showed severe or life-threatening bleeding. Three of nine patients who developed ITP after alemtuzumab therapy, experienced CLL progression requiring chemo-immunotherapy after 3, 4 and 13 months from ITP onset, respectively. One patient achieved a partial remission of CLL with ITP resolution, while the other two died of disease progression. In the remaining six cases, ITP was not associated with disease progression and was treated with corticosteroids and/or intravenous immunoglobulins. Five patients achieved normal platelet counts, while one patient did not respond.

Low-dose alemtuzumab (theoretical cumulative dose 540 mg, equal to half of the classic cumulative dose and one-third of the individual dose) is an effective, safe and well tolerated treatment for CLL, as reported by several recent studies (Cortelezzi et al, Leukemia 2009; Brit J Haematol 2011). In our cohort of CLL patients treated with alemtuzumab, the incidence of ITP was 14.8% that is almost three times higher than previously reported in CLL. These data may indicate a role of T-lymphocyte dysregulation induced by alemtuzumab in the pathogenesis of ITP. Our data also suggested the importance of monitoring platelet counts during follow-up in patients treated with low-dose alemtuzumab for both haematological and non-haematological diseases.