From: matus [matus@snet.net]
Sent: Sunday, March 03, 2002 9:13 PM
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Subject: MFD List - Cancer clusters: findings vs. feelings
(cancer)(statistics)(brokovich)

Cancer clusters: findings vs. feelings
----------
Health Facts And Fears
by David Robinson
   Investigations into proposed environmental cancer clusters
   are unlikely to confirm environmental hazards as a source
   of human cancer. For some people, though, no scientific
   study is ever sufficient reassurance. (02/01/02)
http://www.free-market.net/rd/689075688.html

http://www.healthfactsandfears.com/featured_articles/feb2002/clusters020102.
html

Cancer Clusters: Findings vs. Feelings
February 1, 2002

By David Robinson

Should sixty-nine families in Toms River, NJ receive over $13 million in
settlement money from two chemical companies and a water company? The
families claim the companies are responsible for increased illness rates,
but scientists aren't so sure.

The fear that industrial pollution, present in trace amounts in the
environment around us, may be causing "cancer clusters"-local areas where
cancer is more prevalent as a result of cancer-causing pollutants-has
received a great deal of attention recently. Films such as Erin Brockovich
and A Civil Action have helped bring clusters to the forefront, and
community concern over possible clusters has led to congressional mandates,
federal investigations, and an increase in public sensitivity to the issue.

Defining "Clusters"

While the public typically thinks of cancer clusters in terms of cancer
caused by industrial pollution, scientists tend to see the issue
differently. Robert N. Hoover from the National Cancer Institute defines a
cancer cluster as a geographic area, time period, or group of people with a
greater than expected number of cases of cancer. Epidemiologists-scientists
who study the causes and distribution of human diseases-expect cancer rates
to vary slightly from year to year and use statistical tests to determine
whether or not a given rate is different enough from the average to qualify
as unexpected.

The public and the media, on the other hand, often use the term "cancer
cluster" in a more general way. When members of a community believe that the
number of cancer cases in their community is abnormally high, they will
often seek an explanation for the "cancer cluster." Thus, the term is often
used by the public and the media to refer to the perception of an elevated
number of cancer cases, and by epidemiologists to refer to confirmation of
this perception.

The "Bull's-eye" Problem

A variety of factors often work together to create the appearance of a
cluster where nothing abnormal is occurring. Looking for clusters is
analogous to drawing a bull's-eye after you have thrown darts at the wall at
random. In this situation, there is possibly a place in which a bull's eye
can be drawn that will leave multiple darts in close proximity to some
common center.

The definition of what geographic area is to be investigated in a cancer
cluster study is often problematic. If the hypothesis that cancer rates in a
certain area may be elevated provides the initial impetus for the study, the
natural temptation is to study only the area that includes the cases that
inspired the study. This problem is called "pre-selection bias" because it
involves researchers pre-selecting the geographic area of a study based on
what they already know an investigation of certain areas would reveal.

The problem of "drawing the bull's-eye" applies not only to space but to
time. A study of two clusters in one Ontario town noted that "...the
tendency is to include all years in which cases were reported [in the date
range chosen for analysis], thereby maximizing, and magnifying, any effect
which may be present."

A third way in which the bull's-eye problem can skew results is in the
selection of which cancer to include as part of a possible cluster. In the
case of possible pediatric cancer clustering in Toms River, New Jersey,
investigators began by looking at every category of childhood cancer and
included in their investigation those categories of cancer whose rates were
significantly elevated in Toms River. The threshold of significant elevation
that was used meant that for every twenty cancer categories examined, one
would qualify as significantly elevated.

Normally, a cancer-causing agent will result in an elevation of a specific
type of cancer. Often in these debates, however, a burgeoning set of effects
is putatively linked to a single cause, increasing the odds of finding a few
diseases the rates of which may be elevated through chance, which then
become the focus of study and public outcry. This is aptly illustrated
through one of the most widely publicized cancer cluster cases in recent
years, the Erin Brockovich case. Dramatized in a major film with Julia
Roberts portraying Ms. Brockovich, an overworked paralegal, the case dealt
with the release of chromium-6 into the Hinkley, California water supply by
Pacific Gas and Electric. The suit blamed the chemical for dozens of
symptoms, from nosebleeds to breast cancer, miscarriages, Hodgkin's disease,
and spinal deterioration. Workers who inhale large amounts of chromium-6
over long periods have been shown to be at elevated risk of developing lung
and sinus cancers. But chromium-6 has never been shown to be related to any
other human cancer, or to be carcinogenic to any degree when dissolved in
drinking water.

Public Pressure

An investigation into childhood cancer in Toms River, New Jersey, provides
insight into the pressures that can work against balanced scientific
inquiry. Toms River is the location of two "Superfund" sites, places the
Environmental Protection Agency (EPA) has designated as a high priority for
clean-up due to the presence of hazardous waste.

A nurse in a Philadelphia pediatric oncology ward noticed that many of her
patients were from the Toms River area, and speculated that an environmental
cause might be elevating the pediatric cancer rates in Toms River. When
parents brought their concerns to the attention of state authorities, in
1996, the state evaluated the cancer rates and found no cause for alarm. A
spokeswoman from the New Jersey Department of Health explained that the
state, based on existing data about cancer rates, did not think a
comprehensive cluster investigation would be economical or useful, because
the numbers of childhood cancers were "not statistically meaningful."

Nonetheless, the state moved to address community concern with a series of
investigations into possible sources of cancer risk, including the Superfund
sites. The parents brought a sense of urgency to the discussion. "This is a
terrible disease, and these kids suffer.... These kids don't have time to
wait. I have two other children, and I'm scared to death," said one mother
of a childhood cancer victim.

"In my heart and in my mind, I have no question. Now, it's up to the
scientists to use logic and common sense to get at the truth," said Linda
Gillick, chairwoman of a citizen's committee organized to address the issue
and the mother of another cancer victim.

Where parents were certain, scientists were not. The data on cancer rates
that was available when community members first raised concerns did not show
more cancer than scientists might have expected to be found in a random
distribution in Toms River. Residents prevailed on their congressional
representatives to ask federal officials for an investigation that state
health officials said would be futile. Ultimately, the study was undertaken
as a joint effort between state officials and the federal Agency for Toxic
Substances and Disease Registry.

Problems with Data Collection

Scientific studies linking elevated cancer risk to environmental causes have
generally involved years-long latency periods between exposure to
carcinogenic factors and development of cancer. The latency problem surfaces
in two ways in community-inspired cancer cluster investigations.

First, some of the people who were exposed to the environmental chemical
under investigation may have moved away from the area before the
investigation began. Second, it is possible that some of the cancer cases
that occur within the investigated area may not be attributable to the local
environment. If some of the people who are diagnosed with cancer moved into
the area shortly before being diagnosed, steps must be taken to assure that
their cancer cases are not attributed to local causes.

Chance

As discussed above, the nature of random distributions is such that some
amount of clustering may be expected to occur simply by chance. It is
conventional among scientists to regard an elevated cancer rate as
"statistically significant" if chance alone would produce as much or more
elevation less than 5% of the time. With this criterion, if one examines the
cancer rates in 100 neighborhoods, and cancer cases are occurring randomly,
one should expect to find about five neighborhoods with statistically
significant elevations.

Geography as Symptom

When a group of people who live in geographic proximity to one another
exhibit an elevated rate of cancer, the rate may reflect characteristics
other than geography that those in the affected area share. Characteristics
like similar diets and exercise patterns may tend to be geographically
"clustered" because low-income people who eat disproportionately more fatty
foods live near one-another, because health-conscious suburbanites live in
the same neighborhood, or because rates of smoking tend to differ from one
community to the next. In any of these cases, a geographic cluster might be
proved to exist even if there were no chemical carcinogen in the
environment.

Proving a Negative-Never Say "Never"

No matter how many possible environmental cancer causes are contemplated, it
will always remain possible that some heretofore ignored chemical in the
environment is elevating cancer rates. Thus, investigations of possible
environmental causes for cancer can be extended almost indefinitely, as more
and more possible carcinogens are examined.

For all these reasons-the many ways in which a "bull's-eye" can be drawn,
problems of latency, the lack of reportability of cancer, the similar
behaviors and backgrounds of people who live near one another, and the
vagaries of chance-investigations into proposed environmental cancer
clusters are unlikely to confirm environmental hazards as a source of human
cancer. For some of the fearful, though, no scientific study is ever
sufficient reassurance.

David Robinson, currently a sophomore at Princeton University, was an ACSH
intern in the summer of 2001.


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