Bortezomib: new indication. Second-line treatment of myeloma: limited efficacy, major risks.

(1) When multiple myeloma relapses more than one year after initial treatment, the median survival time is only 12 to 15 months. (2) Bortezomib is a cytotoxic agent that inhibits the 26S proteasome, a complex involved in intracellular protein breakdown in mammals. Bortezomib was initially licensed for the treatment of myeloma after multiple treatment failure; its indications were subsequently modified to include second-line treatment. (3) Second-line bortezomib therapy has not been compared with haematopoietic stem cell grafting, a treatment with documented efficacy. (4) An unblinded comparative trial involving 54 patients requiring second-line treatment showed that bortezomib at a dose of 1.3 mg/m to the 2nd power (twice a week for two weeks, followed by a 10 day rest period) was significantly more effective than a dose of 1 mg/m to the 2nd power in terms of the median survival time (not determined in the 1.3 mg group, versus 26.7 months in the 1 mg group) and the median time to disease progression (11.7 versus 4.2 months). (5) Among 251 patients in whom first-line treatment had failed, bortezomib was significantly more effective than dexamethasone: the one-year survival rate was 80% versus 66% on dexamethasone, and the progression-free survival time was 6.2 months versus 3.5 months. (6) Adverse effects occurred in 30% to 60% of patients enrolled in clinical trials, and were severe in about 10% to 20% of patients. They mainly included fatigue, nausea and vomiting, diarrhoea, anaemia, thrombocytopenia, and peripheral neuropathy. Animal studies indicated a possible risk of cardiotoxicity, and cases of cardiac arrhythmias and conduction disorders were observed in clinical trials. (7) Bortezomib is metabolised by the cytochrome P450 isoenzyme CYP3A4, with a high risk of interactions. (8) The vials contain an excessive amount of this costly drug, creating a risk of inadvertent overdose and leading to unnecessary waste. (9) In practice, bortezomib is an alternative to steroid therapy for patients with multiple myeloma in whom first-line treatment has failed and who do not qualify for stem cell grafting. The choice of treatment must be discussed with the patient, after providing thorough information on the likely benefits and risks