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June 1, 2000
Breast Cancer: Cause and Controversy
Statistical Significance
Epidemiologist Prehn at the Northern California Cancer Center has done one of the more definitive studies to date on Bay Area cancer rates.
It has done little to quell the concern.
Her straightforward approach was to look at the proportion of Marin women with known cancer risk factors and compare that to other counties.
In simple terms, the exercise was designed to find out whether the distribution of known risks, rather than something peculiar about Marin, could account for the high rates of breast cancer there, using easily accessible, existing data to find out.
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The data so far just dont show there's any environmental substance or other factor that could account for Marin breast cancer rates." | |
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Weighing numbers
Results showed that while breast cancer incidence was nine percent higher in Marin than the other 24 counties, established risk factors and markers of high risk -- such as number of children borne and socioeconomic status -- appeared to account for the difference.
That means, they determined, more women with a high risk (as currently understood) for breast cancer live in Marin than elsewhere, but living in Marin County in and of itself does not seem to add to anyone's risk.
Still, Prehn and West did not claim to have answered that lingering question of just what is causing the disease.
In the researchers' own estimation, their simple exercise did not dig deeply enough to accomplish that.
"While this study shows that geographic variation in breast cancer rates in the greater San Francisco Bay Area may be explained by geographic variation in risk factors," they concluded, "it did not directly address environmental causes of breast cancer. The results suggest that environmental risk factors specific to Marin County are not responsible for the locally elevated breast cancer incidence rates. However, the present findings do not imply that there are no environmental risk factors for breast cancer."
Broadening scope
The research so far offers conflicting signals as to just what these environmental risks might be. But as of now nothing points to any factors that may be different in the Bay Area.
So Prehn and West advised broadening the scope of environmental studies to take in "widespread environmental exposures rather than an exposure specific to Marin County."
Nationally, several other researchers have found that regional discrepancies in breast-cancer rates can be explained pretty well by known risk factors and demographic descriptors.
But numbers do change. The latest NCCC cancer statistics show Marin's rates to be even higher, relatively speaking, than the rates used in the 1998 study.
And 10-year-old census data may no longer be accurate, particularly for dynamic regions like the Bay Area.
Although the Prehn study has not satisfied everyone by a long shot, a local physician said the results fit well with his understanding of what is causing his patients' cancer.
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Looking for possible toxins in Marin, perhaps from abandoned Navy facilities or manufacturers, is worth doing, Crowley said.
He just wants a little perspective. An environmental culprit in breast cancer is "worth looking for, but one doesn't need to look any harder in Marin than in other communities. There's no particular reason to suspect there's been more toxic contamination in Marin, and in fact I suspect there has been less."
Next: Digging Deeper
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Breast Cancer: CAUSE & CONTROVERSY by Carl Hall photographs by Pico  SIDEBARS: Photo Gallery: Breast cancer survivors carry on. (Pico) Long Island: A mammoth research effort and its critics. (Hall) Risk factors offer questions and answers. (Wilson)
Toxic Links: How do we know if a chemical is dangerous? (Wilson)
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