Response to paper on ovarian cancer in the Million Women study

The Million Women Study (MWS) has reported new data on the risk of ovarian cancer in postmenopausal hormone users(1).

The study showed a 20% increase in risk when current users were compared with never users. No increase in risk was recorded in women using HRT for less than five years, and past users had the same risk as never users. Risk did not vary significantly with types of HRT.

While the data derived from the MWS are not much different from several other studies, such as the Nurses' Health Study, the Women's Health Initiative study did not show an increased risk of ovarian cancer(2). The IMS would like to comment:

• Following the previous analysis of the MWS on breast and endometrial cancers there were many reservations concerning the methodology and these are still pertinent (3).
• Most epidemiologists would consider that a relative risk of 1.2 is of minimal clinical significance but will inevitably reach statistical significance with very large numbers.
• Risk is far better reported in absolute numbers rather than relative risk or percentage. The absolute risk for ovarian cancer in the MWS was only one extra case per 2500 women after five years and mortality was one per 3300 over five years.

It is most regrettable that the risks for all gynaecological cancers have been added together to produce an estimated increase in risk of 62% for hormone users. Endometrial cancer should be prevented by combined hormone therapy and adding percentages is inappropriate and will inevitably cause further unnecessary distress to the many women who are benefiting from HRT.

References

1. Million Women Collaborators. Ovarian cancer and hormone replacement therapy in the Million Women Study. Lancet 2007; published online April 19th
2. Anderson GL, Judd HL, Kaunitz KM et al. Effects of estrogen plus progestin on gynecologic cancers and associated diagnostic procedures: the Women's Health Initiative randomized trial. JAMA 2003; 290: 1739-48
3. Farmer R. The Million Women Study – is it believable? Climacteric 2005; 8: 210

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