The synthetic progestin MPA, not estrogen, likely caused the small increase in breast cancer incidence in the WHI study's CEE plus MPA group.

“no I'm not I'm not concluding wouldn't it be that the mpa was the difference yes it's the mpa”

“even under the worst conditions possible which was the conditions of the Women's Health Initiative where for all Reasons I'm not going to go into now because I'll have a dedicated podcast that will focus exactly on all the issues around the Whi yes we should you should you even saw in that situation only an absolute increase in risk of 0.1% and that was only in the incidence of breast cancer in the women receiving conjugated acin estrogen and MPA both products that we are not using today”

“the conjugated equine estrogen group alone had breast cancer not only that they almost achieve statistical significance by 0.2 of a P value for a reduction in the incidence of breast cancer an effect that also has persisted for over 20 years”

“secondly there was no increase in breast cancer mortality right so which by the way that lasted that effect lasted till today we still follow those women and we can see that no more of them have died of breast cancer than their counterparts”

“So the absolute risk increase for these women was 0.1%.”

“it is true that in the CE plus MPA group The Root the that group had five cases of breast cancer per thousand women compared to four cases of breast cancer per thousand women in the placebo group and it is true that that's a 25% increase in the relative risk but of course the absolute risk is .1%”

“interestingly the women in the CE alone group had a lower risk of developing breast cancer so the study was halted and the headline read estrogen incre increases the risk of breast cancer by 25% well this wasn't correct um it is true that in the CE plus MPA group The Root the that group had five cases of breast cancer per thousand women compared to four cases of breast cancer per thousand women in the placebo group and it is true that that's a 25% increase in the relative risk but of course the absolute risk is .1% there was no difference in breast cancer mortality in other words there was an extra one case of breast cancer but there was no difference in uh breast cancer mortality those data by the way have been updated every decade or so and we now have like 19-year followup on that group and that fact Still Remains True to this day there is still no difference in the mortality of breast cancer in the CE plus MPA group but you see it would be impossible to make the case that estrogen is the cause there when in the other group you saw the exact opposite effect you saw that the CE group alone had a lower incidence of breast cancer and eventually even a lower mortality due to breast cancer”

“I think most people who think about this problem today acknowledge that it's probably the mpa that was driving the very very small clinically insignificant but statistically significant increase in breast cancer incidents that had no translation to a mortality difference”