Between 2003 and 2007, a person living in SLO County was more likely to develop cancer than he or she would in all but one other county in the state, according to the California Cancer Registry. During the same time period, the county had the eighth highest rate of invasive cancer—or cancer that has spread into healthy tissues. Why is this? The best guess is it’s the people, not the area that puts this county at risk.
The numbers can be quite startling at first, particularly when looking at a Cancer Registry map that color codes counties using a terrorism-like scale ranging from cool yellow (depicting low cancer incidence rates) to holy-crap red (high rates). On such a map, SLO County glares as a giant red blotch in a sea of calm yellow and light orange.
Some possible explanations: It might be because the county has an elderly population. But the Cancer Registry’s numbers are age-adjusted, which is a fancy way of saying any age-related factors are washed away.
It also seems easy to dive headfirst into the conspiracy pool: Maybe it’s the Diablo Canyon nuclear power plant or windblown sand from the Oceano Dunes.
Dr. John Morgan, a Cancer Registry epidemiologist, really doesn’t give much credit to the raw, amalgamated numbers. According to Morgan, there are myriad factors that might warp the data and make SLO County appear to have a higher cancer rate. For one, he said, it doesn’t make sense to lump the statistics for all types of cancer together. He thinks SLO County has a high cancer rate not because of environmental factors but because of the demographics.
“It’s not where you live,” Morgan said. “It’s who lives where.”
In other words, if you live in SLO County, you’re more likely to get cancer, on average. But if you lived anywhere else in the state, you’d probably be just as susceptible. Morgan explained that non-Hispanic whites have one of the highest incidence rates of invasive cancer than other racial groups in California. SLO County has a high population of white people compared to the rest of the state—therefore the appearance of a high rate of cancer.
According to the U.S. Census Bureau, non-Hispanic whites accounted for 73.1 percent of the population in SLO County, compared to just 42.3 percent of the statewide population.
When the Tri Counties area—SLO, Santa Barbara, and Ventura counties—is analyzed based on monochromatic incidences of cancer, the risk on the Central Coast is higher than the statewide rate (451.2 incidences of invasive cancers per 100,000 people versus 433.6 incidences per 100,000). However, in every invasive cancer type—lung, colon, breast, prostate, and pancreas—non-Hispanic whites were most at risk in California.
There was an effort to further analyze local cancer incidences in 2001 when an independent group including the Environmental Center of SLO County reviewed cancer rates by zip code and concluded there was a higher rate of prostate cancer in Arroyo Grande, said Pam Heatherington, now chair of the SLO County Health Commission and formerly of ECOSLO. However, “the study was debunked,” and later retracted, County Epidemiologist Ann McDowell said.
But Heatherington argues the results were too quickly cast aside by epidemiologists, who claimed the high rates merely reflected an elderly population.
“I remember distinctly that the zip code statistics were more eye opening than I had ever seen,” Heatherington said. “We hit so many brick walls about people explaining away any increase that was evident [in the data].”
Asked about the lack of area-specific studies, Morgan thinks there’s really no reason to analyze further.
“Where do you go from here?” he said. “We have not found a problem. We have not found a cancer excess. We have found an excess of non-Hispanic whites, and I don’t see that as a problem.”
This article appears in Mar 25 – Apr 1, 2010.