Hormone therapy: why even doctors feared it for twenty years

On the ninth of July 2002 a press conference in Washington changed the lives of millions of women. Most of them have never heard of it.

That day the authors of the large American Women's Health Initiative study announced they were stopping one of its arms early. The reason: among women taking combined hormone therapy they had found a higher incidence of breast cancer.

The news went around the world in a single day. Within a year prescriptions for hormone therapy fell by more than half in some countries. Women threw their packets in the bin. Doctors stopped offering it. And that reflex is still there in consulting rooms today.

The trouble is that what the public took away from that day does not match what the study actually measured.

What the number looks like when you read all of it

The headlines spoke of a twenty-six percent increase in risk. That figure is true. It is what is called relative risk, and on its own it says almost nothing.

In absolute terms it looked like this: among ten thousand women on combined therapy there were eight additional cases of breast cancer a year. Eight in ten thousand.

The same study also found seven more cardiac events, eight more strokes and eight more pulmonary embolisms per ten thousand women a year. And at the same time six fewer cases of colorectal cancer and five fewer hip fractures.

None of this means the risks are not real. It means they can be discussed in concrete terms. And that a sentence about twenty-six percent and a sentence about eight women in ten thousand land very differently, even though they describe the same thing.

Who was actually being measured

The second thing that did not make the news was the age of the participants. The average age of the women in the study was sixty-three. A large share of them were ten or more years past menopause when they started therapy.

That is a completely different situation from a fifty-year-old with hot flushes who is not sleeping and is weighing up therapy now. Later analyses suggested that timing matters a great deal, and that distinction was exactly what got lost in the original message.

And hormone therapy is not one thing

The study looked at one specific combined preparation at one specific dose, taken as tablets. Today there are different formulations, doses and routes of delivery, and they do not behave the same way. Worth noting: the arm of the same study in which women took estrogen alone did not show a raised incidence of breast cancer.

What to take from it

Not that the therapy is harmless. The risks are real and in some women they are the reason not to prescribe it.

Rather this: if someone answers you in a single sentence, whether it is that it is dangerous or that it is perfectly fine, they are not talking about your case. A good answer sounds different. It asks about your family history, your symptoms, what bothers you most, and only then talks about numbers.

The decision about hormone therapy is yours. But it should be yours on the basis of the whole number, not the headline.

This is information, not medical advice. Therapy is always decided by a doctor together with you.

We devote a whole seminar to this topic, with an hour on it and room for questions. Seminars are held in Czech.