Also, no, the rate is not attributable to the
local population’s high percentage of older
women whose age puts them at the most risk.
That factor is also taken into account and the
statistics specifically age-adjusted.
As for the pet theory that in our highly educated, affluent population more women are apt to
seek routine screening, and hence more cancers
are discovered — no, there is no “detection bias”
in the county. Approximately 70 to 80 percent of
women in Marin get tested regularly, a percentage
in line with or slightly higher than in other counties
throughout the state; at most, that factor accounts
for just a couple of additional cases per year.
Screening itself is an evolving issue: As a
recent New York Times Magazine article points
out, the rising prevalence of breast cancer testing in recent decades, fueled in part by aggressive
early-detection campaigns (“If you haven’t had a
mammogram, you need more than your breast
examined”), may have led some women to view
mammograms as a means of not just finding
breast cancer but essentially curing it. A fair
amount of medical controversy persists regarding
mammography’s benefits and limitations. Some
tumors caught by the test are so slow-moving
that they might never actually metastasize, scientists say; meanwhile, the method is not always
effective at detecting the most lethal forms of the
disease when they’re still at a treatable phase.
Mammography is “a most imperfect test, but
the best one out there at this moment,” says Dr.
Francine Halberg, a radiation oncologist with
the Marin Cancer Institute at Marin General
Hospital, who has addressed the president’s
Breast Cancer Commission and been selected
as one of the country’s top doctors by Who’s Who
in North America, Good Housekeeping, Redbook
and Ladies’ Home Journal.
THE SMOKING GUN
Over the past decade or so, Marin has seen an
unquestionably dramatic drop in breast cancer incidence. And in a correlation that’s rarely
so clear-cut in scientific data, removal of one
identified risk factor seems to have helped bring
about this measurable decline.
In 2002, the Women’s Health Initiative deter-
mined that combination hormone replacement
therapy — generally taken by women with their
uterus intact to combat symptoms of menopause
— was contributing to the incidence of breast
cancer. Subsequent investigation indicated that
Marin women were particularly hard-hit on this
issue because they have among the lowest per-
centages of hysterectomies in California, and
combination HRT was recommended for women
who had not had their uterus removed (women
post-hysterectomy take a different HRT regimen
that does not appear to increase cancer risk).
There is evidence that more affluent women are
less likely to undergo a hysterectomy than less
affluent women, and preliminary data shows that
this is also true in Marin.
It turns out that women in Marin are also
particularly receptive to health messaging, and
when word got out that when it came to breast
cancer risk, combination HRT was more or less
akin to throwing water on a grease fire, they lis-
tened. And they abruptly stopped the therapy.
As the M WS had collected specific informa-
tion on what type of HRT women were using,
the study was poised to show both a striking
downward trend in the type of hormones taken
by Marin women and a concomitant drop in the
breast cancer incidence rate. With a two-year
reporting lag, when the 2003 Marin rate came
out in 2005, it was already significantly lower.
And as time went on and additional statistics
were reported, the HRT-related risk appeared
to further decrease.
“It’s encouraging that some of our excess risk
appears to have been lifted by this simple change,”
notes Dr. Matt Willis, Marin’s Public Health
Officer, who has a master’s in public health and is
a former clinical instructor at Harvard Medical
School and epidemiologist at the CDC.
Brand-new statewide comparative breast
cancer rates, reporting data from 2006 to 2010
(there is always a reporting lag of several years),
just came out t wo months ago. According to the
most recent five-year data from the California
Cancer Registry (the same organization that
reported the alarming rates back in the 1990s),
for white women, Marin’s breast cancer inci-
dence rate is now approximately 8 percent higher
than California’s as a whole — but we are not
alone; other counties such as Yolo, Santa Clara
and San Mateo ranked just as high. Analysis of
that same data based on three-year rates, from
2008 to 2010, while possibly affected by vari-
ables like small population sample and size, show
that incidence in Marin is even more in line with
California rates. Within Marin, high rates of
breast cancer do not vary widely by location, and
to the extent that there are areas of high and low
incidence, they do not appear to occur with any
particularly relevant clustering pattern.
Comparing breast cancer risk in Marin to risk
in other counties is itself problematic, Willis adds,
as “there is no other county similar to Marin.”
While that’s true enough subjectively, it’s also
accurate demographically. Wealthy communities
are generally characterized by city limits rather
than by county boundaries, while statistics are
reported by county; Halberg suggests that one
of the reasons the reported incidence of breast
cancer is higher in Marin may lie in the method
of collecting the data, pointing out that communi-
ties with similar demographics have similarly high
breast cancer rates.
Though it is difficult to make annual rate
comparisons with other counties due to Marin’s
unique demographics, individual studies com-
paring Marin to other sub-county areas with
similar socioeconomic risk factors have found
incidence rates similar to Marin’s. For instance,
county epidemiology expert Ereman points to
research showing that breast cancer incidence in a
high-income section of Contra Costa County was
similar to Marin’s. “However,” she says, “it’s not
that clear cut.” In a November 2012 Breast Cancer
Mapping Project report, researchers identified
four areas of concern in the state: northern San
Francisco, West Los Angeles, South San Francisco
and Orange County — and not all of these commu-
nities can claim higher income levels.
And finally for the national picture, while the
mortality rates have improved, Marin’s breast
cancer incidence is unfortunately not much dif-
ferent than earlier reported numbers. According
to the latest National Cancer Institute data for
white women, Marin and other high-ranking
counties in California have a breast cancer inci-
dence for 2006–2010 about 20 percent higher
than that in the rest of the country.
In 1994, the Northern California Cancer Center released
a report revealing that Marin County had the highest
incidence rate of invasive breast cancer in the world.
