FRANKFURT, March 9 (Reuters) - Shares in Roche

dropped more than 5% on Monday as the Swiss drugmaker failed to

show that its promising drug candidate giredestrant against a

common form of breast cancer can help newly diagnosed patients.

At 0846 GMT, the stock was down 5.1% at its lowest in about

a month.

A phase III trial did not provide reliable evidence that the

drug's use in combination with Pfizer's ( PFE ) Ibrance as a first

treatment slows disease progression when compared with a

standard hormonal therapy plus Ibrance, Roche said in a

statement.

That marked a reversal of fortunes for the oral compound.

The Roche pill last year cut the risk of tumour recurrence

in breast-cancer patients who had received the established

initial treatment in a late-stage trial, boosting Roche's

shares.

The giredestrant pill belongs to a drug class known as oral

selective oestrogen receptor degraders (SERD) to fight tumours

that grow in response to oestrogen, accounting for up to 80% of

all breast cancer cases.

The market opportunity has also attracted AstraZeneca ( AZN )

, which is developing rival compound camizestrant.