(Corrects to "Tagrisso" from "Sargasso" in paragraphs 6 and 7)

April 12 (Reuters) - An independent panel of experts advising the U.S. Food and Drug Administration did not back the accelerated approval of Clovis Oncology Inc's lung cancer drug.

The panel voted 12-1 in favor of waiting for the results from an ongoing late-stage trial that compares the drug's effect to that of chemotherapy.

The drug, rociletinib, is designed to treat a subset of patients with advanced non-small cell lung cancer whose condition has worsened despite treatment.

Clovis is looking to secure accelerated approval for the drug, which allows a company to conditionally market a drug based on early evidence of clinical benefit.

Rociletinib targets patients with a genetic mutation known as T790M that helps tumors evade current lung cancer pills.

A similar drug from AstraZeneca Plc , Tagrisso, won accelerated U.S. approval in November.

Panelists said existing data on rociletinib did not adequately characterize its benefit-risk profile over existing treatments, especially in relation to Tagrisso, and expressed uncertainty about the proposed dose.

Some experts also raised concerns about whether the ongoing late-stage study on rociletinib was designed to answer these questions.

The FDA is not obligated to follow the panel's recommendations, but it typically does so.

On Friday, FDA scientists raised questions about whether rociletinib was superior to existing treatments.

They had also suggested that the drug carry a black-box warning, the strictest warning imposed by the FDA, of increased heart risk.

If approved, rociletinib will likely play second fiddle to Tagrisso, given that its efficacy compares poorly with that of AstraZeneca's treatment, Piper Jaffray analyst Charles Duncan wrote in a late February note.

Clovis' stock was halted on Tuesday on account of the meeting.

(Reporting by Natalie Grover and Amrutha Penumudi in Bengaluru; Editing by Savio D'Souza and Don Sebastian)