Gemtuzumab ozogamicin on the PBS

A new treatment for acute myeloid leukaemia (AML) is now available on the Pharmaceutical Benefits Scheme (PBS). Gemtuzumab ozogamicin is listed for the treatment of previously untreated de novo CD33-positive AML, in combination with standard intensive chemotherapy. It is not PBS subsidised for patients with acute promyelocytic leukaemia (a rare subtype of AML).

Gemtuzumab ozogamicin is an antibody-drug conjugate. It consists of a CD33 monoclonal antibody linked to a cytotoxic calicheamicin derivative. The CD33 cell surface antigen is present in 85-90% of patients with AML. Once gemtuzumab ozogamicin binds to CD33, the complex is internalised, and the calicheamicin portion of the antibody-drug conjugate is released. Once activated, the calicheamicin causes double-stranded DNA breaks, which can lead to cell cycle arrest and apoptosis.

The ALFA-701 trial investigated the safety and efficacy of daunorubicin and cytarabine with or without gemtuzumab ozogamicin. The primary endpoint of event-free survival (EFS) was significantly higher for patients treated with gemtuzumab ozogamicin (median 17.3 months, compared to 9.5 months in the control arm).

Permanent discontinuation due to treatment-emergent adverse effects was more common in the gemtuzumab ozogamicin group (31.3% compared to 7.3% in the control arm). The most common reasons for discontinuation were thrombocytopaenia and hepatobiliary disorders. Severe myelosuppression affected the majority of patients in each group. However, the median time to platelet recovery was significantly longer in the gemtuzumab ozogamicin group.