Corcept Therapeutics Incorporated has announced encouraging initial efficacy data from its Phase I/II trial of mifepristone in combination with the chemotherapy drug, eribulin, in patients with glucocorticoid receptor, or GR,-positive, metastatic, triple-negative breast cancer, or TNBC. Corcept is investigating whether the addition of mifepristone, the active ingredient in Corcept's approved medication, Korlym, will enhance the effect of eribulin in patients whose TNBC tumors express GR, one of the receptors to which Korlym binds. The trial is being conducted in two parts.

In the first phase, researchers determined the maximum tolerated combined dose of mifepristone and eribulin. This dose - 300 mg of mifepristone daily with 1.1 mg/m2 of eribulin taken on days one and eight of a three week cycle - is now being administered to patients in the trial's second, efficacy phase, which will enroll 20 patients with GR-positive, metastatic TNBC. This Phase of the trial is ongoing.

At SABCS, the trial's investigators presented efficacy data from the 15 patients enrolled to-date with GR-positive TNBC who have been treated with the recommended dose (two patients from the trial's first phase and 13 from its second). As determined using the Response Evaluation Criteria in Solid Tumors (RECIST), initial efficacy results in this group were as follows: one patient exhibited a partial response (defined as a 30% or greater reduction in tumor size), seven had stable disease and five had progressive disease. Two patients were too early in their treatment to be assessed.

The combination of mifepristone and eribulin has been well-tolerated. Most adverse events have been disease-related and of mild or moderate severity, with the most common being neutropenia, fatigue, hypokalemia, nausea, hair loss and neuropathy. Neutropenia has been manageable with the administration of growth factor.

No patient has suffered a serious adverse event. Pharmacokinetic data show no interaction between eribulin and mifepristone.