Clinical Efficacy of Bortezomib Based Therapy in Plasma Cell Leukemias.

Introduction Plasma Cell Leukemia (PCL) is characterized by a high number of plasma cells in peripheral blood (>2 × 10⁹/L) and more than 20% of circulating plasmocytes on differential count. Primary PCL or secondary form, after previous multiple myeloma (MM), represent the most aggressive forms of clonal gammapathy with very poor outcome from both conventional chemotherapy and autologous or allogeneic transplant. For this reasons new effective treatment approaches are required. The proteasome inhibitor Bortezomib has been shown to be effective in advanced MM with a rapid response but few reports have been published regarding its potential role on PCL. We report here the clinical results of a serie of PCL patients that received proteasome inhibitor, Bortezomib (Velcade®), as induction therapy.

Patients and Clinical Results We describe 10 patients with PCL treated with Bortezomib. Median age was 58 y (30–70). 4 cases were primary, de novoPCL and 6 cases were secondary forms of relapsed or progressive MM. Patients with secondary PCL had received a median of 3 previous lines of therapy including autologous transplantation (5 cases). Bortezomib at standard dose iv: 1.3 mg/m2 days 1,4, 8,11 every 21 days were used alone in 2 patients and in combination with high dose of Dexamethasone +/− Adryamicin in the rest. 3 cases recived the BDD scheme (Bortezomib iv, Pegylated Doxorrubicin iv and oral Dexamethasone). 9 patients were evaluable for drug efficacy with 7 cases showing some grade of favourable response with the first cycle, including 3 cases of CR. 4 patients have died: 1 during first weeks and 3 for progression, 2–3 months after initial response. 3 cases received allogeneic transplant with related donor and reduced conditioning and are alive 12, 14 and 30 months postransplant. The median follow up since PCL diagnosis of 6 alive patients is 14 months (3–39 months). 3 patients received maintenance therapy that included low dose thalidomide. Grade 2 thrombopenia, neutropenia and gastrointestinal symptoms were the main secondary toxicity. No complicated tumoral lysis syndrome were observed.

Conclusions and Comments Bortezomib has been shown to be effective by several mechanisms in patients with MM resistant to multiple previous treatments and as induction therapy alone or in combination with other drugs. The favourable responses observed in these cases of PCL; including de novo patients, and the biological ex vivo results in PCL cell lines, suggest the potential efficacy of this agent combined with dexamethasone and doxorubicin. Although more experience is necessary these data support future trials with Bortezomib combined with other drugs for example BDD scheme in the induction treatment of PCL. The role of allogeneic intensification therapy has also to be investigated in young patients after control of PCL with this approach. For maintenance of response, the role of this drug or other new drugs as thalidomide or lenalidomide has to be investigated.