AstraZeneca’s experimental medicine selumetinib failed to keep a common form of lung cancer at bay in an advanced clinical test, making it the second drug maker to report a setback in battling tumors of the lung this month.

The drug, combined with chemotherapy, didn’t help patients live longer or prevent the disease from worsening, the two goals being sought by researchers in the trial, the London-based drug maker said in a statement on Tuesday.

Bristol-Myers Squibb Co. said Friday its cancer medicine Opdivo failed in a study that would have been the basis for widely expanding its use, sending the stock of the US drug maker plummeting. Bristol-Myers, AstraZeneca, and others are betting on a new generation of treatments that harness the immune system to battle cancer and kindle sales growth. Unlike Opdivo, selumetinib isn’t one of those.

The study results are disappointing but the financial impact will be ‘‘negligible,’’ AstraZeneca spokeswoman Karen Birmingham said in an e-mailed response to questions.

Not so for Array BioPharma Inc., which sold the rights to the drug to AstraZeneca in 2003. The company’s shares fell 18 percent to $3.65 in trading before US exchanges opened. Under the agreement, Array stood to receive development milestones and royalties on product sales.

Analysts predicted the treatment would have annual sales of $287 million by 2021, based on the average estimate compiled by Bloomberg. Goldman Sachs Group Inc. analysts said in a note to clients they hadn’t included selumetinib in their revenue estimates.

AstraZeneca is working on immunotherapies that may challenge Bristol-Myers’s Opdivo. The experimental treatment durvalumab, for example, may be worth investigating in combination with selumetinib, according to Birmingham.

Treatments for lung cancer could represent a market of $10 billion to $15 billion a year in developed economies, Tim Anderson, an analyst at Sanford C. Bernstein LLC, estimated in a report this week.

AstraZeneca is also studying selumetinib for some forms of thyroid cancer as well as a genetic disorder known as neurofibromatosis type 1. A year ago, the company said the treatment had failed in a trial for uveal melanoma, a rare disease in which cancer cells form in the tissues of the eye.

In the 510-patient study, selumetinib was under review as a second-line treatment for a form of non-small-cell lung cancer known as KRAS mutation-positive that was either advanced locally or that had spread.