Roche said today it would discontinue a late-stage study of an experimental Alzheimer's drug after it failed to prove effective, underlying the difficulty of treating the memory-robbing disease.

The Swiss drugmaker also said a breast cancer trial had failed to demonstrate the benefit of adding its new drug Kadcyla to treatment programmes. Although both projects were relatively risky, the news is a double blow for Roche, which in recent years has boasted one of the most productive research pipelines in the industry.

Shares in Roche fell more than 3 per cent in early trading. The setback for Alzheimer’s drug gantenerumab is particularly disappointing, since there had been hopes that giving it in the phase three study to patients with so-called prodromal disease, or pre-dementia, would produce a better outcome.

Many scientists believe the best hope for treating Alzheimer's lies in giving drugs at this earlier stage, before patients' brains are wrecked by the condition. Alzheimer's, the most common form of dementia, already afflicts 44 million people worldwide and this figure is set to triple by 2050, according to campaign group Alzheimer's Disease International. Unlike heart disease and cancer, which have seen major strides in drug development, no new therapies have been approved to treat Alzheimer's in a decade.

Roche suffered a setback with another experimental Alzheimer's drug earlier this year, but the company insisted it was not giving up. "This is the first phase three trial to evaluate a potential disease-modifying medicine in this early prodromal stage of Alzheimer's disease. We remain committed to investigating new medicines for this devastating illness," said Roche chief medical officer Sandra Horning.

Gantenerumab continues to be studied in another phase three trial involving patients with later stage disease and Roche has two other experimental Alzheimer’s drugs in phase two tests, crenezumab and RG1577.

Separately, Roche’s late-stage study in women with previously untreated advanced HER2-positive breast cancer showed three of its treatments helped people live without their disease worsening. However, the two treatment arms containing Kadcyla did not prove superior to other approaches in terms of improving the time patients lived without their disease progressing