Human Genome Sciences' ( HGSI) shares were tanking in the premarket session Wednesday after the company reported disappointing clinical trial results from an experimental lupus drug.

The company found during a Phase II trial that LymphoStat-B was safe, well tolerated and showed signs of a clinical effect in patients. However, the drug didn't meet the overall primary endpoints of reducing the signs and symptoms of lupus at the 24th week or increasing the time to the first instance of the disease's flare-up to more than 52 weeks.

Shares of Human Genome were sinking $3.94, or 28%, to $10.03 before the opening bell.

LymphoStat-B reduced the symptoms of what is called systemic lupus erythematosus at week 52 and reached a level of statistical significance in seropositive patients, a subgroup that represented 75% of the study's patients, Human Genome said. Planning for a Phase III trial is underway.

About 90% of the people diagnosed with lupus are women. Symptoms can include extreme fatigue, painful and swollen joints and kidney problems. Lupus can lead to arthritis, heart and lung inflammations and central nervous system problems, among other complications.

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