Phase-I/II study to evaluate dose limiting toxicity, maximum tolerated dose, and tolerability of bendamustine HCl in pre-treated patients with B-chronic lymphocytic leukaemia (Binet stages B and C) requiring therapy

Purpose: Bendamustine hydrochloride, an anti-neoplastic agent with unique mechanism of action, is known to cause impressive remissions in relapsed nonHodgkin’s lymphoma and chronic lymphocytic leukaemia (CLL). Optimal bendamustine dosing for CLL patients had not been finally established and a phase I/II study was conducted to determine the maximum tolerated dose (MTD) and dose limiting toxicity (DLT) of bendamustine. Methods: The open-label, single-centre phase I/II study was conducted from March 2001 to September 2002 in Sofia, Bulgaria. The 15 study patients were extendedly pre-treated, but fludarabine-naive (3 female, 12 male, 47–72 years of age, 61 years on average). Bendamustine was given at a starting dose of 100 mg/m² on days 1 and 2 every 3 weeks based on the previous results in lymphoma. Results: Bendamustine was well tolerated in spite of heavy pre-treatment of the study participants. Toxicity corresponded to the known safety profile of bendamustine, with the exception of bilirubin elevation. The level of 110 mg/m² was established as MTD. A bendamustine dose of 100 mg/m² is the recommended dose for further clinical investigations. A 4-week interval is recommended to allow for sufficient recovery. Efficacy results confirmed powerful anti-neoplastic activity of bendamustine even in extendedly pre-treated CLL patients. Based on the remission criteria, nine patients were defined as responders (four CRs, two PR, three NC) and two patients as nonresponders to therapy. Four patients were not evaluable for response, because they had received less than three courses bendamustine. After a follow-up period of 15 months, the four patients with CR were still in remission. One patient with PR had relapsed, the other had ongoing response. Conclusions: Bendamustine is a very active and well-tolerated drug in patients with pre-treated and refractory CLL. Fludarabine-naivity of patients appears to markedly improve their bendamustine tolerability. First-line use of bendamustine is a safe option for CLL-patients requiring treatment, because bendamustine—owing to its unique pharmacodynamics—(1) is highly effective, (2) reasonably safe, and (3) does hardly produce cross-resistance against other anti-neoplastic drugs effective in this indication.