Rituximab As an Effective Salvage Therapy in Pretreated Hairy Cell Leukemia Patients: The Bologna Experience

Hairy cell leukemia (HCL) patients usually experience multiple disease relapses during the course of their disease. The CD20 antigen is highly expressed on the surface of hairy cells. Single-agent rituximab can be a suitable treatment options in patients relapsing after repeated courses of purine analogs, if purine analogs are contraindicated (e.g. in case of poor bone marrow cellularity, high disease infiltration predicting long-lasting aplasia), especially if newer agents (such as moxetumomab or vemurafenib) are not easily available (as it happens in several countries).

Our institutional series of HCL patients receiving single-agent rituximab as salvage therapy was retrospectively reviewed. Patients received rituximab at the standard dose of 375 mg/m² weekly for 4 weeks. The main study objectives were overall response rate (ORR), time-to-next treatment (TTNT), progression-free survival (PFS) and overall survival (OS). Responses have been categorized according to the Consensus Resolution Criteria.

Thirty-three patients received 39 courses of rituximab (4 patients received it twice, one patient three times), in median as third line of therapy (range 2-8). First rituximab was given at a median age of 61 years and at a median time from disease diagnosis of 65 months. Out of 39 courses, a complete response was obtained in 28.2% of cases, a partial response in 23.1% and a minimal response in 20.5%, yielding an ORR of 71.8%. In 28.2% of patients we observed no response. Median TTNT was reached at 33 months (65% at 2 years), while median PFS was reached at 24 months (51% at 2 years). Median OS resulted of 154 months (22% at 20 years). Among the 5 patients receiving rituximab more than once, all responded after the first course, although the ORR after the second or later course was only 50%. Median TTNT following the first rituximab was 38.5 months in these patients, ranging from 15 to 205 months.

To our knowledge, this is the widest series of HCL patients receiving single-agent rituximab for disease relapse. Rituximab is an effective salvage therapy in pretreated HCL patients after failure of purine analogs, as it permits an adequate disease control with considerably long TTNT periods. It may be repeated if no alternatives are available, although it seems to reduce its efficacy in the following courses.

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