PARIS (REUTERS) - French healthcare company Sanofi said it would stop further work on amcenestrant, once seen to have large potential against breast cancer, after a second trial failure dealt a major blow to its drug development prospects.

The move puts more pressure on Sanofi to bolster its drug development pipeline, as it grows increasingly dependent on its multi-billion best seller, eczema and asthma treatment Dupixent, and after it fell far behind in the race to develop Covid-19 vaccines.

A trial dubbed Ameera-5, which was testing amcenestrant on women with newly diagnosed advanced breast cancer, was stopped early because an independent monitoring panel found no signs of it working.

"All other studies of amcenestrant, including in early-stage breast cancer (Ameera-6), will be discontinued," Sanofi said.

The company previously said the drug candidate's biggest commercial opportunity was as a treatment early after diagnosis.

"This was a flagship drug in the pipeline and an important oncology asset," wrote Credit Suisse analyst Jo Walton.

Sanofi said the drug, which was used in combination with Pfizer's established Ibrance in the study, "did not meet the prespecified boundary for continuation", when compared to a group of patients in the trial on standard hormone therapy.

Amcenestrant belongs to a drug class known as selective oestrogen receptor degraders (Serd) that fight tumours that grow in response to oestrogen, which are estimated to account for up to 80 per cent of all breast cancer cases.

The market opportunity for oral Serds has attracted a range of drugmakers. Sanofi's rivals, including Roche and AstraZeneca, are working on similar pills, known as giredestrant and camizestrant, respectively.

The drugs are designed to work like AstraZeneca's established injectable breast cancer drug Faslodex, while offering a less burdensome route of administration.