To the Editor: We urge caution about the recently published findings of Durna and colleagues on use of hormone replacement therapy (HRT) by breast cancer patients.1 They found no increase in risk of breast cancer recurrence or reduction in life expectancy in women using HRT after treatment for primary breast cancer, leading them to conclude that HRT seems a safe treatment for women with a history of breast cancer. We believe that their study has many limitations and consequently their conclusions are unfounded

Durna's group conducted a retrospective, observational study using unmatched patient groups. The HRT group was statistically younger, with smaller tumours and fewer positive nodes, and thus had better prognosis. The authors discussed regression analyses for age of diagnosis and stage to reduce potential bias, but did not include these data.

The omission of tumour grade and receptor status in the analysis is an obvious flaw. The mean duration of HRT use was short compared with many previous studies (mean, 1 year). This is particularly important, as any risk is likely to be cumulative.2 There were also statistically more women in the HRT group who had received HRT before diagnosis, and for a longer duration (mean, 6.5 years v 3 years). This too may bias results, as breast cancer that develops after HRT has been suggested to carry a better prognosis.3 There was also no subgroup analysis of those who took concomitant tamoxifen.

Durna and colleagues also do not address the concerns raised by the Women's Health Initiative study, which showed an excess of cardiovascular and thromboembolic events in "healthy" women taking HRT.4 Many of these events occurred in the first years of HRT use, the time assessed in Durna's study. The risks of short-term HRT in breast cancer patients may be not only tumour-related, but may also include cardiac and thrombotic events, which were not specifically considered by Durna and colleagues.

Of additional concern is the extensive portrayal in some sections of the media that this study is conclusive regarding the risks of HRT use by women with breast cancer. The importance of correct media interpretation of studies is discussed in the accompaning editorial by Patel and colleagues.5 Despite this editorial and the inadequacies of Durna's study, the results of this study, released through the media, inaccurately suggested safety and even a possible benefit of HRT.6 This simply adds to the "HRT furore".

All studies addressing this issue to date have been small and non-randomised, often with no control group or unmatched groups.2 Because of these limitations, no clear recommendation can be made about the safety of HRT in women with breast cancer. Until results are available from rigorous randomised controlled trials, such as the ongoing HABITS (Hormone Replacement Therapy After Breast Cancer — Is It Safe?) study (IBCSG 17-98), we should not be "advocating" HRT to breast cancer patients. For Durna's group to suggest otherwise is very premature. In addition, there are well studied, effective alternatives to HRT for treating menopausal symptoms in breast cancer patients (eg, venlafaxine),7 and these would seem the current safer option.