AstraZeneca this morning said that postmenopausal women taking the gold-standard tamoxifen for early breast cancer may significantly reduce their risk of recurrence by switching to the company’s new aromatase inhibitor, Arimidex (anastrozole), according to results of two combined studies published today in The Lancet.

Industry observers already believe that tamoxifen’s crown will be stolen by the likes of Arimidex, Novartis’ Femara (letrozole) and Pfizer's Aromasin (exemestane) [[22/04/05g]]. Data published at the end of last year showed that five years of treatment with AstraZeneca's drug was more effective than the standard five-year tamoxifen therapy in terms of survival [[09/12/04b]]. And these new results, a combined analysis of the Austrian Breast & Colorectal Cancer Study Group and Arimidex-Nolvadex trials, demonstrated that patients who switched to Arimidex after two years of therapy with tamoxifen, rather than continuing on tamoxifen, saw a 40% reduction in the risk of recurrence, and a 39% reduction in the risk of distant recurrence at a median follow-up of 28 months.

“We already have confirmation from the ATAC trial that initiating women on Arimidex as early as possible helps to ensure the best protection against recurrence in the first two years immediately after surgery,” commented Mr Giles Cunnick, Consultant Breast Surgeon at Wycombe Hospital. “The ABCSG and ARNO trials confirm that those patients who have not had the advantage of starting their adjuvant therapy with Arimidex immediately following surgery can still gain significant benefit if they switch therapy from tamoxifen to Arimidex.”

AstraZeneca says Arimidex is the only aromatase inhibitor with data both for the full five-year setting and for a switch part way through a course of tamoxifen. It will be hoping this is enough to help it capture the largest slice of the pie in this highly competitive arena. Sales of Arimidex in the second quarter alone jumped 50% over the comparable quarter last year to edge over the $1 billion-dollar mark [[29/07/05d]].