In November, 1993, a perceived increase in cancer incidence for a small geographic area in Moreland, Idaho, was reported by a concerned resident of the area to the Cluster Analysis Work Group (CAWG), Idaho Division of Health. The geographic area of concern consisted of a one-mile radius circle surrounding an abandoned dump site located at approximately 225 N 800 W, Moreland (Bingham County, Idaho). An increase in cancer incidence was thought to have occurred in recent years, beginning 1980. Because population data were not available for the circle as defined by the resident, the area studied was the most similar geographic area for which population data are available. This analysis area (census block group 3, BNA 9506; and blocks 188, 189, 192, 193 and 194, BNA 9503) mirrors as closely as possible the boundaries of the circle.
On April 27, 1994, a meeting was held at the Moreland Elementary School to discuss the proposed protocol to be followed by the CAWG for Moreland. The meeting was attended by area residents, state legislators, Bingham County Commissioners, Division of Environmental Quality staff, Southeast District Health Department staff and Division of Health staff. The following points were agreed upon:
The results of the analysis showed that fewer cases of cancer were observed for the Moreland analysis area than were expected based upon comparison rates from Bingham County and the state of Idaho. It was concluded that the Moreland analysis area did not experience elevated cancer incidence between 1980 and 1992. Because of the interest in the results, the Division of Health agreed to reanalyze the data periodically, as information on newly diagnosed cases became available to the Cancer Data Registry of Idaho (CDRI). This report reflects reported cancer incidence data from January 1, 1980 to December 31, 1995.
Using data from the CDRI and the Bureau of the Census, cancer incidence among Idaho residents was analyzed. Cancer incidence in the Moreland analysis area was compared to the incidence for Bingham County and the state of Idaho for the years 1980-1995. Cases of benign disease were excluded from the analysis. The data elements used were primary cancer site code, histology code, age at diagnosis, sex, and residence at diagnosis. Person-years (a measure of the length of time a person is at risk for disease), the standard denominator for incidence rates, were estimated for the Moreland analysis area, Bingham County, and the state of Idaho by multiplying the 1990 census population by a factor of 16, the number of calendar years in the time frame of interest. This method for estimating person-years assumes that the population growth rates have been similar from 1980-1995 in the Moreland analysis area, Bingham County, and the state of Idaho. Rates were calculated for total cancers, and for each site with three or more cases in the Moreland analysis area during 1980-1995 (breast, lung, brain, colorectal, and prostate). Statistical tests were used to calculate the probability that the Moreland analysis area experienced more, or less, cases of cancer than would be expected based upon Bingham county and state rates. P-values, the probability of a difference as or more extreme than the ones found between the Moreland analysis area and Bingham County and the state, were calculated two-tailed.
This report is descriptive in nature; no discussion of potential etiologies for various cancers is included. Residence at the time of diagnosis was used for the analysis. Persons may have resided in locations other than Moreland, Bingham County, or the state of Idaho for most of their lives, but been diagnosed with cancer after moving to one of these areas. In such circumstances, conditions in these areas would likely be unrelated to cancer etiology.
Forty (40) cases of malignant/invasive/in-situ cancer were diagnosed among residents of the Moreland analysis area between January 1, 1980 and December 31, 1995. This compares to 63,574 cases and 1,719 cases, respectively, occurring in the state of Idaho and Bingham County during the same time period. The cases in the Moreland analysis area by primary site include seven female breast, five lung, four brain, four colorectal, three prostate, and one or two cases among several other sites.
The table, Comparison of Cancer Incidence Among Moreland Analysis Area, Bingham County, and the State of Idaho, 1980 - 1995, shows the 1990 census population, estimated person-years (1980 - 1995), number of cases, and crude cancer incidence rates for the Moreland analysis area, Bingham County, and the state of Idaho. Persons in the Moreland analysis area experienced significantly fewer cases of total cancer than would be expected based upon the state rate (40 versus 68 cases expected; p=.0004). There were no statistically significant differences between the number of cases of breast, lung, or colorectal cancer for residents of the Moreland analysis area and either Bingham County or the state of Idaho. Persons in the Moreland analysis area experienced significantly more cases of brain cancer than would be expected based upon Bingham County or state rates (4 versus 1 case expected; p=.0155 compared to Bingham County, and p=.0094 compared to the state of Idaho). Persons in the Moreland analysis area experienced significantly fewer cases of prostate cancer than would be expected based upon the state rate (3 versus 10 cases expected; p=.0256).