Cancer Incidence Rates in Eddy and Lea Counties

New Mexico, 1970-1994

Brain and Nervous System Cancers

Brain and other nervous system cancers are relatively uncommon in the US; the NCI estimated that 17,500 new brain and other nervous system cancers were diagnosed in the US in 1993 (NCI 1993). In 1994 in New Mexico, 94 in situ and invasive brain cancers and 3 in situ and invasive nervous system cancers were diagnosed, comprising about 1.4% of total cancers (NMTR 1996).

Males are diagnosed with this cancer 1.5 times more often than females (NCI 1993). Risk factors for brain cancer are not well understood. However, possible risk factors include exposure to ionizing and electro-magnetic radiation, exposure to certain chemicals such as organic solvents and pesticides, and having a family history of brain cancer.

Nationally, brain and other nervous system cancer incidence rates have increased slightly over the last several decades, from 5 per 100,000 in 1973 to 6.3 in 1990 (NCI 1993). In New Mexico, incidence rates for brain and other nervous system cancer increased slowly from 1970 to the mid-1980s, and then began decreasing (Figure 13). While rates have not substantially changed overall from 1970 to 1994, they have varied for individual years, ranging from a low of approximately 4 per 100,000 in 1980 to a high of 5.5 in 1986. Statewide rates for males and females combined were generally lower during the period studied than comparable rates for the US (NCI 1993).

Spatial Variation

Spatial variation of incidence rates for brain and other nervous system cancer, for the period between 1970 and 1992, among residents of New Mexico, Eddy County, and Lea County, is presented in Tables 14, 15 and 16.

Non-Hispanic Whites: During the period studied, the incidence rate of brain and other nervous system cancers among non-Hispanic white males and females combined was 5.6 per 100,000 statewide, and ranged from a low of no cases in Harding County to 13.6 in Rio Arriba County. Incidence rates among non-Hispanic whites in Eddy and Lea counties were below the corresponding statewide rates.

Hispanic Whites: During the period studied, the incidence rate for brain and other nervous system cancers among Hispanic white males and females combined was 3.8 per 100,000 statewide, and ranged from a low of no cases in Catron, Roosevelt, and Union counties, to a high of 13.4 in Los Alamos County. Incidence rates of brain and other nervous system cancers were below corresponding statewide rates among Hispanic white males in Eddy and Lea counties.

Temporal Variation

Temporal variation of incidence rates for brain and other nervous system cancer, for the period between 1970 and 1994, among residents of Eddy County and Lea County is presented in Figures 14 and 15.

By Sex: Statewide, incidence rates of brain and other nervous system cancers increased slightly among males during the period studied, from approximately 4.3 per 100,000 in 1971 to 5.5 in 1993, and decreased slightly among females from approximately 4.5 per 100,000 in 1971 to 3.3 in 1993. Incidence rates for brain and other nervous system cancer among males were generally higher than among females statewide, but in Eddy and Lea counties, rates were similar among both sexes. In Eddy County, brain and other nervous system cancer incidence rates decreased slightly among males and increased slightly among females. In Lea County, the incidence rates decreased slightly among males, and did not substantially change overall among females. However, rates among both sexes in Eddy and Lea counties varied widely (by as much as 7 times).

By Ethnicity: Statewide, incidence rates of brain and other nervous system cancer did not substantially change overall among non-Hispanic whites or Hispanic whites during the period studied. In general, incidence rates among non-Hispanic whites were higher than among Hispanic whites. For many of the years studied, no cases of brain or other nervous system cancer among Hispanic whites were reported in either county.

Factors Affecting Rates: Increases in diagnoses of brain cancer between 1970 and 1994, especially among older people, may be due to new medical imaging techniques (NCI 1993). These techniques include Computerized Axial Tomography (CAT), in use in the mid-1970s, and Nuclear Magnetic Resonance Imaging (NMRI), in use in the late 1980s. Before the development of these techniques, some deaths from brain tumors may have been misclassified as strokes.