Plerixafor. Only for certain patients when G-CSF stem cell mobilisation fails

Filgrastim, a recombinant G-CSF, is the standard drug used to mobilise haematopoietic stem cells for collection prior to autologous transplantation in patients with lymphoma and myeloma. Plerixafor, a CXCR4 receptor antagonist, is now authorised in the European Union for use in combination with G-CSF when stem cell mobilisation with G-CSF alone is unsuccessful. Clinical evaluation is based on two comparative trials with similar designs. In a trial in 302 myeloma patients, the G-CSF-plerixafor combination was associated with a statistically significantly higher rate of successful mobilisation, defined as collection of at least 6 x 10(6) CD34+ cells after one or two apheresis sessions, than a combination of G-CSF and placebo (71.6% versus 34.4%). The same effect was observed in a trial involving 298 lymphoma patients, in which the CD34+ cell target number was at least 5 x 10(6) after a maximum of 4 apheresis sessions (59% versus 20%). In these trials, the addition of plerixafor to G-CSF increased the frequency of injection site reactions (55% versus 36%) and was associated with twice as many gastrointestinal disorders (diarrhoea and nausea or vomiting). There was no difference between the combined treatments in terms of disease-related mortality at one year (about 8%). However, longer follow-up is needed to ensure that plerixafor does not lead to disease aggravation by mobilising malignant cells. Given the long-term uncertainties, plerixafor should be reserved for patients in whom G-CSF alone fails to yield a sufficient number of stem cells required for transplantation.