Shares of Array BioPharma Inc. jumped in premarket trading Tuesday after the drug developer said its potential allergic asthma treatment fared much better than a placebo in mid-stage testing.

The Boulder, Colo., company said the oral treatment, labeled ARRY-502, helped improve a measure of lung function when tested in 184 patients in the United States with mild-to-moderate persistent allergic asthma. Array said the results support continued development of the drug, and it is seeking a partner to help with that.

Late-stage clinical testing is the last phase before a drug developer submits a product to regulators and is the most expensive part of development. Array has no products on the market producing revenue, but it also is developing potential treatments for cancer and diabetes.

The company estimates that there are about 12 million U.S. patients with mild-to-moderate persistent allergic asthma. A statement from Array said ARRY-502 is the first oral, non-steroidal treatment since Singulair to demonstrate “clinically meaningful activity” in allergic asthma cases.

Singulair brought in about $5.5 billion in annual sales for Merck & Co., the world’s third-biggest drugmaker by revenue, until its U.S. patent expired last August. That leads to competition from cheaper generic drugs.

Shares of Array jumped 17.8 percent, or 99 cents, to $6.55 in pre-market trading. It has traded in a range of $3.25 to $6.56 in regular trading over the past year.