Brain cancer rate in normal range, study finds
Al Musella's Comments: (This is his personal views and are not necessarily the views of the Musella Foundation!)
Posted on: 09/16/2004
Brain cancer rate in normal range, study finds
By EVE BYRON - IR Staff Writer - 09/16/04
Lewis and Clark County residents do suffer a high incidence of brain cancers, but the numbers are still within the normal range for Montana and the nation and don't constitute a "cancer cluster," according to a study released Wednesday.
State Epidemiologist Todd Damrow also noted that the age-adjusted incidence rate of all types of brain cancer in the county is "higher than in neighboring counties and other Montana counties with large populations" and also is above the overall state and national rate.
However, he said, the magnitude of difference isn't extraordinary.
"I guess the good news is that we don't feel that Helenans are at a greater risk of getting brain cancer," Damrow said on Wednesday. "Our overall observable rates are not out of whack with the expected rates."
But Damrow cautions that some data from 2003 and 2004 haven't been released yet, so he recommends that his office should continue to analyze brain cancer incidence data as it become available, and that Lewis and Clark County should continue to monitor rates in the upcoming years.
"The complex nature of cancer makes it inherently challenging to identify, interpret and address cancer clusters," he said. "The time between exposure to a cancer-causing agent, or the existence of some other risk factors, and the development of cancer can be decades; therefore, causes are hard, and in some cases impossible, to identify."
Damrow launched his investigation into brain cancer rates in Lewis and Clark County in March at the request of the local health department, after an oncologist at St. Peter's Hospital reported observing what he believed was a high incidence of aggressive brain tumors among area residents.
Using data collected from death certificates from 1990 to 2002, Damrow's investigators found that the death rate due to brain cancer in Lewis and Clark County was higher than the statewide death rate in some years and lower in others.
On average during the 13-year period, the rate was 5.8 deaths per 100,000 persons per year in the county compared to 4.9 deaths statewide. The national death rate due to brain cancer during the same period was 5.6.
Those averages included a high of seven reported cases in 2000 and a low of only one in 1996.
The investigators also looked specifically at the brain tumors noted by the oncologist — "glioblastoma multiforme," "astrocytoma" and "oligodendroglioma" tumors, which are aggressive brain tumors. These traditionally occur in people between their late 30s to mid 60s and usually are fatal, with death within three months of diagnosis without treatment, and within 1-3 years with surgery, radiation and/or chemotherapy.
Damrow said their study showed that the "age-adjusted, type-specific brain cancer rate among Lewis and Clark County residents is higher than in neighboring counties and other Montana counties with large populations."
But the 21 diagnoses of these three types of brain tumors from 1998 to 2002 — about 7.5 cases per 100,000 person years, compared to 4.9 cases per 100,000 person years statewide — "doesn't extend beyond the expected range for the population.
So overall, the occurrence of cases of brain cancer in the county is in the expected rate for the population, and the recent cases aren't indicative of a cancer cluster, Damrow said in his report issued Wednesday.
Joan Miles, county health officer, said they appreciate the state's help on the investigation.
"The suggestion that something unusual was happening in our community obviously had us really concerned," Miles said. "It's a relief to know that we do not have higher rates of this type of cancer than would normally be expected."
Still, Damrow is quick to acknowledge that the investigation, which used figures from the Montana Central Tumor Registry as well as from death certificates, comes with a number of qualifiers.
Perhaps most important is that no information on brain tumors from the registry was available for 2003, which is the year the oncologist reported seeing higher numbers of a specific type of brain tumor in patients.
In addition, Montana's small population makes statistical sampling difficult. So when Damrow's investigators tried to break reported cases into specific areas within Lewis and Clark County — using zip codes — the statistics couldn't support theories of brain cancer cases within any particular area.
"Valid conclusions cannot be made from data containing such small numbers," Damrow said.
And finally, Damrow cautioned that so called "cancer clusters" are notoriously difficult to figure out. More often than not, seemingly high rates are just a statistical blip. Or it may be that one community has a greater number of cases, and another has fewer; or one year produces more cancers than another year. Either way it often averages out in the end.
Some experts note that anywhere from 85 to 90 percent of possible cancer clusters that are investigated end up being normal rates that people just happen to notice or chance groupings of a disease.
"Cancer is unfortunately more common than many people realize," Damrow added. "According to the American Cancer Society, one out of every three Americans will develop some form of cancer during their lifetime. Given this rate of occurrence, it's not uncommon for cases to seem to appear in groups within a county, town, neighborhood or workplace."
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