US regulators have turned down Aveo Oncology's kidney cancer drug tivozanib, saying the data package is inconclusive and requesting a new study.

The US Food and Drug Administration has issued a complete response letter informing Aveo that it will not approve in its present form the New Drug Application for tivozanib as a treatment for advanced renal cell carcinoma. Specifically, the agency stated that the "inconsistent progression-free survival and overall survival results and imbalance in post-study treatments make the TIVO-1 results uninterpretable and inconclusive when making a risk-benefit assessment".

The FDA goes on to recommend that Aveo conduct an additional clinical study to support approval of tivozanib for the treatment of advanced RCC. The letter comes as no surprise, given that last month, the FDA's Oncologic Drugs Advisory Committee voted 13 to one against approving the drug. Panellists were concerned that, while matching progression-free survival, there may be a reduction in overall survival with tivozanib when compared with Bayer's Nexavar (sorafenib).

Shares sank after the FDA panel vote and just last week Aveo announced a restructuring which will see its workforce slashed by 62%, with 140 staff being laid off. Partner Astellas said it would not proceed with a European filing for tivozanib or finance future clinical trials in RCC so Aveo has given up on the drug in that indication.

However, it will continue with two Phase II trials testing tivozanib for colorectal and breast cancer and it expects to have enough cash for at least two years.