There has been a long-simmering controversy over breast cancer rates in Marin County, California. Marin County is one of the wealthiest counties in the United States and also has one of the highest breast cancer rates — 198 cases per 100,000 population compared to a national average of 139 per 100,000 for the rest of the country.
Activists who believe that pollution is a major contributor to breast cancer seized on this cancer cluster as evidence for their views, although a number of alternative explanations were possible. But now it turns out that there is an even better explanation — the data that claimed Marin County had a breast cancer incidence of 198 cases per 100,000 population appears to have been faulty.
The faulty data came to light after research in 2002 said that the rate of cancer for white women in Marin County had increased from 191 cases per 100,000 in 1998 to 230 cases per 100,000 in 1999. That sort of massive jump was extremely suspicious.
It turns out that such estimates had been using faulty data from the U.S. Census Bureau that dramatically undercounted the population of women in Marin County. Census data from 2000 showed that the 1990 estimates that such studies had been using underreported the number of white women 45-64 in Marin County by close to 20 percent. Revised breast cancer rates have not been released.
Ironically, another recent study of breast cancer among women in Marin County will also not please the activist who want pollution to be the cause and accuse researchers of “blaming the victim” anytime another cause is put forward.
A study by researchers at the University of California, San Francisco and published in the online journal Breast Cancer Research found a strong correlation between alcohol consumption and breast cancer among women in Marin County. Women who consumed two drinks a day had twice the breast cancer risk, and the risk increased with self-reported alcohol consumption.
That study was small, comparing 285 Marin County women with breast cancer to 286 healthy women living in the county. But it did find no correlation between breast cancer and length of time living in Marin County, suggesting the high breast cancer rate in Marin County has something to do with a confounding factor that women there share rather than something to do with Marin County itself.
Source:
Marin County breast cancer rates not as high as once thought. Justin Pritchard, Associated Press, April 4, 2003.
Study: Marin breast cancer related to alcohol consumption. Associated Press, May 7, 2003.