What happened

RAPT Therapeutics (NASDAQ:RAPT) stock was crushing it on Monday, with shares skyrocketing 110.4% as of 11:59 a.m. EDT. The huge gain came after the company announced positive top-line results from a phase 1b clinical study evaluating RPT193 in treating moderate-to-severe atopic dermatitis.

So what

You'd expect that RAPT's results from the early-stage study of RPT193 had to be fantastic for the biotech stock to more than double. And they were.

Patients treated with the company's experimental drug achieved a 36.3% improvement in the Eczema Area and Severity Index (EASI) score from baseline. That was more than twice the 17% improvement seen in patients on a placebo.

The story looked even better with patients experiencing a 50% improvement in EASI score -- 42.9% of patients treated with RPT193 achieved this marked improvement compared to only 10% of patients in the placebo group.

Document with atopic dermatitis printed underneath a Diagnosis heading with several pills and a pen on top of the document.

Image source: Getty Images.

RPT193 also achieved the primary efficacy endpoints on two other measurements: the validated Investigator Global Assessment (vIGA) and pruritis Numerical Rating Scale (NRS). The experimental drug appeared to be well tolerated in the early-stage clinical study, with no serious adverse events reported.

Investors were especially excited about these results because RPT193 is a once-daily oral treatment. If the drug eventually wins regulatory approval, it could have a competitive advantage over rival treatments that are administered via injection.

Now what

RAPT Therapeutics now plans to advance RPT193 to a phase 2b study targeting atopic dermatitis. The company will also evaluate the therapy in a phase 2a study in treating asthma.

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