Bayer's regorafenib shows promise in renal cancer, may fuel Onyx dispute

German drug major Bayer Schering Pharma AG has announced results from a Phase II trial of regorafenib (BAY 73-4506), a potent oral multi-kinase inhibitor, which demonstrated that treatment with the compound resulted in a 31% partial response rate and 50% stabilization rate in patients with metastatic renal cell carcinoma (RCC). These data were presented in an oral session at the joint 15th Congress of the European CanCer Organization (ECCO) and 34th Congress of the European Society for Medical Oncology (ESMO).

Regorafenib is a follow-on drug to Bayer and USA-based Onyx' Nexavar (sorafenib), and news of the positive results for the new compound add to its commercial potential, and are likely to fuel the dispute between the partners; Onyx sued Bayer in May over the rights to regorafenib, which Onyx refers to as fluoro-sorafenib, claiming its molecular structure differs from Nexavar, or sorafenib, only in one atom. Bayer expects Nexavar to generate peak annual revenues of $2.9 billion.

At the time of data analysis, 81% of patients (n=48) in the trial experienced disease stabilization or regression. Specifically, 31% of patients (n=15) experienced a confirmed partial response (PR), according to the Response Evaluation Criteria in Solid Tumors (RECIST), and 50% of patients (n=24) experienced stable disease (SD). The data also showed an estimated median progression-free survival of 8.3 months at the time of protocol-defined end of study. Importantly, the time of data analyses, which occurred on May 31, 2009, was prospectively defined in the protocol as when the last patient was treated for at least six months. At the time of analysis, 25 patients remained on treatment and 80% (12 of 15) of patients who achieved a PR had an ongoing response. Two additional patients who were classified as having SD achieved a confirmed PR past the data analysis date, bringing the total PR to 35 percent (n=17) of patients. Study data continue to be reviewed.

The most common drug-related adverse events (all grades) were hand-foot skin reaction (HFSR), fatigue, hypertension, mucositis, diarrhea, alopecia, rash, voice changes, anorexia, nausea, constipation and vomiting.