The pharma giant used the recent European Congress of Clinical Oncology (ECCO) in Barcelona, Spain, to show off the latest Phase III data on ixabepilone for the first time in Europe. The results showed that the drug increased progression free survival (PFS) in metastatic breast cancer patients by 40 per cent - from 4.2 months to 5.8).

The drug works by binding to tubulin, a protein that is forms the basis of microtubules - the cell skeleton or scaffold. By binding to its target, ixabepilone stabilises the cell and prevents it from dividing (they stop in the G2-M phase of cell cycle) and, therefore, a tumour from growing.

Although this mechanism isn't new - indeed BMS's Taxol (paclitaxel) binds to the beta subunit of tubulin - the structure of ixabepilone is new (it is an epothilone B analogue) and therefore it represents a new 'class' of molecules.

The epothilones are derived from Sorangium cellulosum, a myxobacterium first discovered on the banks of the Zambezi River in Africa 20 years ago. The reason scientists are excited about this new class of drug is that, unlike taxanes, the epothilones appear not to be very susceptible to known tumour resistance mechanisms.

This is partly because ixabepilone interacts with different sub-types of microtubules; it is active against the Beta III tubulin isoform, high levels of which are associated with resistance and poor responses to taxanes. The drug also has low susceptibility to mechanisms that confer tumour resistance, such as overexpression of efflux transporters -P-glycoprotein (P-gp) and multidrug-resistance protein-1 (MRP1).

In the phase III study, 752 women with metastatic breast cancer whose tumours were resistant to anthracyclines and taxanes were randomised to ixabepilone in combination with capecitabine or capecitabine treatment alone.

As well as the 40 per cent increase in PFS, more than twice as many patients achieved an objective tumour response with combination treatment than capecitabine alone (35 versus 14 per cent).

The Phase III study on show at ECCO is the first to report superior PFS and objective response following the addition of a second agent to capecitabine, according to principal investigator Jacek Jassem, University of Gdansk, Poland.

A analysis of a subset of patients, who had not received treatment for their metastatic breast cancer previously (they had received chemotherapy in the adjuvant or neo-adjuvant setting), was also completed. In this case, PFS increased from 2.1 patients to 7 months.

"The subset analysis, showed really impressive results when ixabepilone was given as first line therapy for metastatic disease. This creates a rationale for further studies in less pre treated patients and in adjuvant settings," said Jassem.

How impressed the regulators are with this, and other, ixabepilone data will become clear this month; the US Food and Drug Administration (FDA) has granted priority review to BMS' New Drug Application (NDA) and the 'target action date' is set for late October.