Extreme drug resistance is common after prior exposure to paclitaxel

The platinum-free interval (PFI) is an important entity in the treatment of women with epithelial ovarian cancer. The purpose of this study was to determine on clinical samples whether a taxane-free interval (TFI), as defined by in vitro extreme drug resistance assay, existed in women previously exposed to platinum and taxane chemotherapy.

Records were examined from 2003 to 2006 to find all patients with epithelial ovarian cancer who had previous exposure to platinum and taxane therapy. Further examination was done to find all patients who underwent secondary cytoreduction and had their tumor submitted for extreme drug resistance assay.

Thirty-four women meeting the above criteria were found. The mean PFI was 25 months (median 18). The mean TFI was 27 months (median 20). Over 44% of the patients have been exposed to more than just a course of platinum and a course of a taxane. In patients having a PFI of >or=12 months, 38.8% had extreme drug resistance (EDR) to carboplatin and 41.9% EDR to cisplatin. Conversely, in patients having a TFI of >or=12 months, 89.7% had EDR to paclitaxel and 82.8% EDR to docetaxel.

While only a small percentage have EDR to carboplatin and cisplatin after a PFI of >or=12 months, almost 90% of patients with a TFI>or=12 months showed EDR to paclitaxel in vitro.