Sophiris Bio Inc (NASDAQ: SPHS) shares plunged Monday after its development drug for prostate disorders failed to show effectiveness in interim results of a Phase III trial.

Sophiris traded recently at $0.55, down more than 80 percent.

Involving 479 patients, results concerned the first 12 weeks of a year-long study aiming to measure the drug's safety and effectiveness in treating lower urinary tract symptoms of benign prostate enlargement.

Chief Executive Randall Woods said the ongoing study is unaffected by the interim finding, issued by an independent monitoring committee.

Monitors raised no safety concerns in their report.

Woods expects to issue further results when the 52-week study is completed and analyzed in the fourth quarter of 2015.

The interim analysis was conducted for planning subsequent clinical trials.

The drug, PRX302, is designed to be as effective as pharmaceuticals, less invasive than the surgical interventions, and without the sexual side effects seen with existing treatments for benign prostate enlargement.

Sophiris plans to launch a Phase II "proof of concept" study of PRX302 for the treatment of localized prostate cancer by the end of its 2015 first quarter.

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