Was Estrogen-Progestin Hormone Replacement Therapy Responsible for High Rates of Breast Cancer in Marin County?

It certainly looks that way. Read: "Recent Trends in Hormone Therapy Utilization and Breast Cancer Incidence Rates in the High Incidence Population of Marin County, California".

There are three very interesting observations reported in the study. There’s of course the strong correlation between the sharp drop in the incidence rate of invasive breast and the discontinuation of estrogen plus progestin hormone replacement therapy (EPHT). But there’s also the fact that this group of well to do and well educated women apparently picked up on the HERS and WHI study results and almost overnight collectively and dramatically altered their preferences for a medical treatment. And then there’s the discovery that hysterectomy rates varied wildly throughout the various counties in California.

As for the first finding, these and similar results continue to add to the overwhelming evidence that the breast cancer clusters in Marin County, CA and Long Island, NY are not due to environmental pollutants but instead are due to a mix of lifestyle, surgical procedures and medications along with a genetic component.

As for the second and third findings they reinforce the emerging view that comparing cancer rates from one county to those of other counties, to the state as a whole, or to national rates is perilous at best. Here Marin County women adopted EPHT early, did so at a high rate relative to women elsewhere in the state and underwent hysterectomies at a low rate relative to other women yet those causal factors were completely unaccounted for in early studies. As a result, activists and some researchers concluded that the cancer cluster had to do with the environment of Marin County rather than the lifestyle choices of its residents.

One of the underlying assumptions of epidemiological studies is that the population investigated and the group to which it’s compared are the same. These results demonstrate that merely accounting for gender, race and age isn’t enough and that lifestyle choices afforded by education and wealth can make a critical difference, both positive and negative.