John F. Seymour, MBBS, FRACP, PhD, from the Department of Hematology at the Peter MacCallum Cancer Centre in East Melbourne, Australia, discusses the efficacy of single-agent ABT-199 (GDC-0199), a novel Bcl-2 inhibitor, in high-risk relapsed or refractory chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL).
In the phase I trial, 56 patients received treatment with ABT-199 at doses from 150 mg to 1200 mg. The overall response rate for patients treated with ABT-199 was 84% with a complete remission rate of 23%, Seymour notes. In general, 90% of patients had received prior treatment with fludarabine with approximately 50% of patients developing fludarabine resistance. On average, patients received 4 median treatments prior to receiving ABT-199, representing a very heavily pretreated patient population.
Furthermore, Seymour says, response rates were sustained in patients with 17p deletions, which have conventionally indicated a poor response to treatment. In a phase I context, this agent has generated exciting response across poor prognostic groups, Seymour notes.
Although it was not a prospective objective of the trial, local labs completed 4-color flow cytometry. Overall, 8 patients tested negative for minimal residual disease. In the context of a single agent in relapsed and refractory CLL, this agent has demonstrated very encouraging efficacy, Seymour believes.
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