Taking aspirin seven or more times a week reduces the risk of breast cancer by 28%, a study has found (JAMA 2004;291:2433). The drug reduced the risk of hormone receptor positive tumours but not hormone receptor negative tumours.

In an accompanying editorial, Dr Raymond DuBois of Vanderbilt University, Nashville, Tennessee, described the biochemical mechanism by which inhibition of cyclooxygenase by aspirin could result in lower concentrations of oestrogen (JAMA 2004;291:2488-9).

The retrospective, case controlled study looked at women who had new diagnoses of invasive breast cancer or breast cancer in situ from 1 August 1996 to 31 July 1997 in the Long Island breast cancer study …