Women with breast cancer who are eligible for hormonal treatment with AstraZeneca’s Arimidex get a survival boost if Roche’s anti-HER2 antibody Herceptin is added to their therapy, according to new clinical trial results.

The results are significant because it is the first time that Herceptin (trastuzumab) has been tested alongside hormonal therapy in co-positive women, i.e. those who are both hormone receptor-positive breast cancer – accounting for around two-thirds of patients - and also HER2-positive.

Co-positives account for around 16% of the total breast cancer population, and are thought to have a particularly poor prognosis, according to a Roche spokesperson.

The trial, called TAnDEM, compared the combination of Herceptin and Arimidex (anastrozole), an aromatase inhibitor, to Arimidex alone in co-positive post-menopausal women with advanced breast cancer.

Roche said that Herceptin plus Arimidex provided a significant benefit compared to Arimidex alone on progression-free survival, although the actual data will not be released yet as it is due for presentation at the forthcoming European Society of Medical Oncology meeting in late September.

Safety data in both arms of the trial were ‘acceptable’, according to Roche, given the known safety profile of each of the drugs in the advanced breast cancer setting. Patients in TAnDEM will continue to be followed for any side effects.

Once the data are presented at ESMO, Roche will prepare applications to update the labelling for Herceptin with regulatory authorities around the world.

Herceptin has been approved in Europe since 2000 for the treatment of patients with advanced, HER2-positive breast cancer, and earlier this month got the go-ahead for use in early-stage patients.

Herceptin is Roche's third-biggest product, bringing in around $1.8 billion in sales last year, almost 50% ahead of 2004's tally, with approval in early-stage patients expected to add momentum to the drug’s growth. Genentech, which sells Herceptin in the USA, has also filed for approval of the early indication.