Cancer Cluster By Sally Deneen

Erin Brockovich found one. People frequently report them. But it’s much more rare that the epidemiologists searching for cancer clusters confirm one exists.

As you might expect, a cancer cluster refers to a higher-than-expected number of cases of cancer among a given group of people, in a given geographic area, or over a given period of time.

Brockovich was a file clerk in a legal office who uncovered a cancer cluster caused by Pacific Gas & Electric’s hexavalent chromium in the Southern California town of Hinkley. Her story wowed Americans when Julia Roberts brought it to the silver screen in 2000.

Other famous cancer clusters involved scrotal cancer among chimney sweeps in 19th-century England, asbestos miners in Montana, and cancer of the vagina among young women whose mothers were treated with
diethylstilbestrol (DES), a synthetic estrogen.

But actually confirming such a cancer cluster is a tricky thing, according to the U.S. Centers for Disease Control and Prevention. Before even launching what is bound to be a lengthy and expensive investigation, experts ask: Is the rate of cancer within expected limits? How likely is it, given the information available, that a cluster could be pinpointed?

Factors that often weigh against confirmation of such a cancer, the CDC says, include lack of enough cases for a meaningful statistical comparison; assessing people’s exposure to any given agent; and the fact that cancer is often the result of a combination of factors.

Epidemiologists look for cancers of a certain organ when they examine a possible cluster. However, because cancer spreads, or metastasizes, it may be difficult to identify the organ originally affected for a large number of people.

Critics say the system for discovering cancer clusters is biased against confirming them and that, when they are found, too often scientists are unable to pinpoint a cause.

For more info:

-To learn about some cancer clusters currently under investigation or to get more info about the general topic, go to: www.cdc.gov/nceh/clusters. Cancer registries provide oodles of statistics about cancer by state; to get stats for your state, go to Google and search for "cancer registry" and your state’s name.

-Read the National Cancer Institute's FactSheet here: www.cancer.gov/cancertopics/factsheet/Risk/clusters