(Bloomberg) -- AstraZeneca Plc and Daiichi Sankyo Co. failed to win immediate endorsement for an additional use for their breast cancer medicine from England’s drug-cost regulator, a potential blow to the companies’ efforts to expand sales of one of their most promising therapies. 

A committee for the National Institute for Health and Care Excellence said Tuesday that the companies need to provide more information about the benefits of the drug, called Enhertu, in patients with advanced HER2-low breast cancer. The agency acknowledged the drug could provide a major advance for these patients, who have low levels of a protein linked to growth of some breast cancers.

The National Health Service in England already pays for the drug to treat patients who have higher levels of HER2 in breast tumors.

“The committee has identified a number of areas for clarification by the company before its next meeting and NICE will work with the company to address these,” said the regulator, which determines which medicines are cost-effective options for use in the NHS in England. 

The companies are committed to working with NICE and providing additional analysis, a spokesperson for Daiichi Sankyo said by email. In France and Germany the drug is already being funded for use in adults with this specific form of breast cancer, according to the statement. 

$10 Billion

Enhertu has become the star of the class of drugs called antibody-drug conjugates, or ADCs. It’s shown to extend the lives of breast-cancer patients with few treatment options, and analysts have estimated it will generate more than $10 billion annually.

About half of breast cancer patients classified as HER2-negative, or lacking the protein, actually have low levels. The partners have been looking for wider coverage of their drug to treat this broader population, potentially adding to sales.

Britain’s health care system is under increasing pressure as costs spiral amid staff shortages and long waiting lists, affecting patient care. NICE has faced criticism for not recommending blockbuster medicines because the costs seem too high. The agency estimates that about 1,000 people would have been eligible to receive Enhertu.

Last year, NICE published changes to the way it assesses new medicines and other health technologies. While the updated method garnered praise from many health experts, some questioned whether it could cause end-stage cancer patients to miss out on last-resort treatments.

The agency’s new procedures “may underestimate the severity of this disease, which would have met NICE’s previous end-of-life criteria,” the statement from Daiichi Sankyo said.

AstraZeneca shares fell as much as 0.7% and were trading 0.2% higher as of 2:41 p.m. in London. 

Enhertu “represents a potentially significant development for people with this type of advanced breast cancer who currently have limited chemotherapy options and no targeted treatments available to them,” Helen Knight, director of medicines evaluation at NICE, said in Tuesday’s statement. 

(Updates with Daiichi Sankyo comment in fifth, ninth paragraphs.)

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