New data from the landmark IES trial, presented at the European Cancer Organisation/European Society of Medical Oncology meeting in Berlin, showed that postmenopausal women with oestrogen-receptor early breast cancer who switched to Pifzer’s Aromasin after taking tamoxifen for two to three years had an 18% reduced chance of disease recurrence compared to women who took tamoxifen for the full five years.

Lead investigator Charles Coombes, director of the oncology department at Imperial College, London, said: “These findings show that the benefit of Aromasin (exemestane) carries on six years after the switch from tamoxifen providing women with a higher chance of living without breast cancer recurrence and confirming that this strategy provides a durable benefit.”

The IES trial, published in the Lancet two years ago and part-funded by Cancer Research UK, is one of the world’s largest and longest running trials of endocrine treatment in the adjuvant setting. The new findings showed that women who went on to exemestane had a 14% less chance of dying than those who stayed on tamoxifen.

There are over a million cases of breast cancer diagnosed worldwide every year. About 75% are oestrogen-receptor positive. The anti-oestrogen drug tamoxifen is standard treatment after surgery in women who have early-stage breast cancer and is normally taken for five years. Exemestane is an aromatase inhibitor (AI), which interferes with the function of aromatase, an enzyme responsible for the production of oestrogen. The question of how best to use AIs and tamoxifen has been under investigation.

Prof Coombes commented: “The new results from the IES trial now give us the confidence that the switch strategy as used in this trial is a new approach to the treatment of breast cancer.”

Rob Coleman, professor of medical oncology at the University of Sheffield, added that AIs such as exemestane have better toxicity than tamoxifen in terms of gynaecological and thromboembolic effects but the follow-up data from the IES trial did show that exemestane use could increase bone loss, blood pressure and rheumatological effects such as joint stiffness. Prof Coleman said: “There are some disadvantages as with all effective treatment but based on these results, we think the switch strategy is safe and potentially has more advantages because of better efficacy and tolerability than tamoxifen.” By Rhonda Siddall in Berlin