Simple concept helps explain WHI to patients: focus on attributable risk

OB/GYN News,  Oct 15, 2003  by Kate Johnson

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CHARLOTTETOWN, P.E.I. -- One simple change in the way risk is explained could have avoided much of the confusion that still surrounds results published last year from the Women's Health Initiative, according to Dr. Robert Reid.

"Patients have to understand the attributable risk, which is what the risk is in relation to the baseline risk, in order for it to have any meaning," said Dr. Reid, professor of obstetrics and gynecology and chair of the division of reproductive endocrinology and infertility at Queen's University, Kingston, Ont.

Consumer newspaper headlines about the Women's Health Initiative (WHI), warning that hormone therapy (HT) is associated with a 26% increase in breast cancer, misled patients into thinking that their personal risk of breast cancer is 26%. If that risk were explained to them in terms of attributable risk, they would understand that their baseline risk of breast cancer is about 10% and that the addition of combination HT increases that risk by only 1/10 of a percentage point per year, he said at the annual clinical meeting of the Society of Obstetricians and Gynecologists of Canada.

Put another way, for every 10,000 women, an extra eight cases of invasive breast cancer per year could be attributed to HT use, added Philip Hahn of the department of obstetrics and gynecology at Queen's University.

Mr. Hahn described a continuing medical education (CME) course designed by Dr. Reid that is aimed at helping physicians put the risks described in the WHI into perspective.

A questionnaire, designed by Mr. Hahn, measured the reactions of 28 ob.gyns, and 42 family physicians to the trial, as well as the effects of the CME update. A total of 36% of ob.gyns, said they felt that some of their patients had discontinued HT because of media reports on the WHI, and 11% thought that many of their patients had discontinued their medication for this reason.

Seventy-nine percent reported increased anxiety among their patients about HT.

But the CME course helped physicians understand the implications of the report and convinced them that quoting attributable risks, rather than relative risks, was the appropriate way to relay the study results to patients.

"Any relative risk is basically meaningless, unless you relate it back to the baseline risk, and so it's a better reflection of the true risk to relate it in an absolute fashion," Mr. Hahn said.

Before the CME course, 64% of ob.gyns, explained the WHI results to their patients in terms of attributable risks ("eight more breast cancers per 10,000 women annually"), whereas after the course, 93% said they would quote attributable risks.

The premature termination of the combination HT arm of the WHI last year left many physicians in limbo, waiting for experts to comment on the findings, Mr. Hahn said. His survey shows that 64% of both ob.gyns, and family physicians reported that extensive media coverage resulted in general confusion and uncertainty about the appropriate use of HRT. This was largely due to the media's use of relative risk rather than attributable risk, despite the fact that attributable risks were provided in the original article, he said.

The WHI abstract stated that absolute excess risks per 10,000 person-years attributable to estrogen plus progestin were seven more coronary heart disease events, eight more strokes, eight more pulmonary embolisms, and eight more invasive breast cancers.

Absolute risk reductions per 10,000 person-years were six fewer colorectal cancers and five fewer hip fractures (JAMA 288[3]:321-33, 2002).

BY KATE JOHNSON Contributing Writer

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