THE BIG PICTURE
You know the ubiquitous pink ribbon, and you
know the term, but did you know that breast
cancer is actually an umbrella term that encom-passes more than one disease? Subtypes of
cancer of the breast are genetically distinct,
with potentially different causes and certainly
diverse responses to treatment. The National
Cancer Institute defines breast cancer as cancer
that forms in tissues of the breast. Cancer that
remains in the breast’s lobules (milk glands)
or the lining of the milk ducts (thin tubes that
carry milk from the lobules to the nipple) does
not kill. The incidence and mortality rates refer
to invasive breast cancer — cancer that has
spread from the lobules or ducts in the breast
to surrounding tissue.
This year in the United States, nearly a quarter of a million women (and a couple thousand
men) will be diagnosed with breast cancer.
Approximately 40,000 women and 400 men
in the country will die of the disease in 2013.
That’s about 109 women and one man every day.
In 1994, the Northern California Cancer
Center released a report based on data from
SEER (the Surveillance, Epidemiology and
End Results Program of the National Cancer
Institute) revealing that Marin County had the
highest incidence rate of invasive breast cancer
in the world. Within the next half dozen years,
multiple reports, including California Cancer
Registry statistics, revealed that Marin’s incidence rate was not just higher than in any other
county in the state, but much higher — approaching 60 percent more. The media dubbed Marin
the “breast cancer capital of the world,” and, as
might be expected, hysteria reigned. The offices
of Marin County Health and Human Services
were flooded with calls from women asking if it
was safe for them to live in, or move to, Marin.
The data cried out for follow-up questions —
the most obvious being why is the rate higher in
Marin? Was the anomaly explained by specific
demographic factors — screening biases, for
example — or something more insidious — the
air, the water, the land itself? Women wanted to
know, did simply living here put them at a higher
risk of getting the disease? In response, the
community — including members of Congress,
doctors, educators, researchers, local agencies,
county representatives and a slew of concerned
residents — came together to seek some answers.
MYTH BUSTING
First of all, it turned out that due to population
estimates that were later made more precise with
additional information, the incidence rates in the
late 1990s were never actually quite as high as
reported. While the numerator used in the calculation (the number of breast cancer cases) was a
known quantity, the denominator (the population
of the county) was projected from 1990 census estimates. New, 2000 census figures showed the Marin
population at risk was actually larger than anticipated — meaning there were really fewer cases per
capita than reported. Recalculated, the rate was
about 20 percent lower than previously cited.
Within a few years, more information was
provided, much of it from the landmark Marin
Women’s Study (M WS), funded by the Centers
for Disease Control and Prevention. The first
breast cancer research in Marin to link disease
risk factors with biospecimens and outcomes, the
MWS is conducting ongoing analysis of 20-page
questionnaires filled out between 2007 and
2009 by 14,000 women — fully one-fifth of all the
women eligible for breast cancer screening in the
county. In addition, women were spitting for the
cause — donating their saliva so researchers could
search for biological links, says Rochelle Ereman,
head of the Department of Health Services
Community Epidemiology Program.
Right from the start, MWS researchers
identified and screened out multiple biases, or
data-skewing factors, that could account for
the higher rate. To dispel one armchair theory,
no, the rate is not attributable to a mostly white
population: although breast cancer is most
prevalent in Caucasian women, that factor
had already been screened out, and the statistics compare white women to white women. A
small caveat: incidence is indeed higher among
women of Ashkenazi Jewish heritage, and
statistically a slightly high percentage of such
women reside in Marin.
