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Women's and Children's Health

Studies show that obesity affects mammography accuracy and screening rates

Obese women are at greater risk of dying from breast cancer than women who are not obese. Early detection of breast cancer through mammography screening can reduce breast cancer deaths by 20 to 39 percent. Yet, a recent study found that white women who are obese are less likely than non-obese white women to obtain a mammogram. The study was supported by the Agency for Healthcare Research and Quality (HS11683). In addition, obesity reduces the accuracy of mammograms. According to a second AHRQ-supported study (HS10591), obese women had more than a 20 percent increased risk of having false-positive mammography results (indication of abnormalities that further testing showed not to be cancer) compared with underweight and normal weight women. Both studies are summarized here.

Wee, C., McCarthy, E.P., Davis, R.B., and Phillips, R.S. (2004). "Obesity and breast cancer screening: The influence of race, illness burden, and other factors." Journal of General Internal Medicine  19, pp. 324-331.

This study found that obese white women were less likely to undergo breast cancer screening than normal weight women, a relationship not seen in black women. The investigators analyzed data from the 1998 National Health Interview Survey to examine the relationship between mammography use and weight category and the influence of race, illness burden, and other factors on this relationship. They examined the relationship between body mass index (BMI; weight in kg/height in m2) and receipt of breast cancer screening in the preceding 2 years among women aged 50 to 75.

Among the 5,277 eligible women, 72 percent reported mammography use. The rate was 74 percent among white women and 70 percent among black women. Higher BMI was associated with lower screening among white women, with mammogram use lowest in women with a BMI greater than 35 kg/m2 (64 to 67 percent). Moderately obese white women (BMI 35 to 40) were 17 percent less likely to have had a mammogram than normal weight white women. Despite the higher prevalence of known barriers to health care among obese women—such as lower socioeconomic status and higher illness burden—adjusting for these and other factors did not influence the findings.

On the other hand, overweight and obese black women were as likely as or more likely than both black and white normal weight women to report mammography use, a difference not readily explained by differences in sociodemographic factors, health care access, health habits, and other factors. Compared with normal weight black women, mammography use was similar or higher in overweight (BMI 25 to 30), mildly obese (BMI 30 to 35), and moderately obese black women.

The white women in this study with obesity were more likely to have feelings of worthlessness in the preceding 30 days, but black women did not report these feelings. Although adjusting for this alone did not explain differences in screening by BMI, this difference in body image perception may interact with health behaviors, such that white women who are obese may be less willing to undergo mammography. Provider bias may also play a role.

Elmore, J.G., Carney, P.A., Abraham, L.A., and others (2004). "The association between obesity and screening mammography accuracy." Archives of Internal Medicine 164, pp. 1140-1147.

Overweight women have a 14 percent increased risk and obese women have more than a 20 percent increased risk of having a false-positive mammogram compared with underweight and normal weight women, according to this study. Although this difference could be considered small, it is significant at a population level. When screening 10 million obese women, a false-positive rate increase of 2 percent (for example, from 10 to 12 percent) would lead to about 200,000 additional women with false-positive mammography results. An additional $120 million would be required for further tests to evaluate the false-positive results, at an estimated cost of $600 per false-positive result. The increased costs are over and above the anxiety involved for the women.

Achieving a normal weight may improve the accuracy of a woman's mammogram, suggest the researchers. They analyzed 100,622 screening mammography examinations performed on members of a nonprofit health plan. They assessed the relationship between BMI and measures of screening accuracy. Compared with underweight or normal weight women, overweight and obese women were more likely to be recalled for additional tests, after adjusting for factors such as age and breast density.

Overweight women were 17 percent more likely, mildly obese women (BMI 30-34 kg/m2) were 27 percent more likely, and moderately or severely obese women (BMI 35 or more) were 31 percent more likely to be recalled. As BMI increased, women were more likely to have lower mammogram specificity, that is, a lower proportion of women without breast cancer were identified as free of cancer. No significant differences were noted in mammogram sensitivity (proportion of women with breast cancer identified as such by the mammogram) related to women's BMI.

Editor's Note: Another AHRQ-funded study on a related topic found that rates of recent screening mammography and Pap smears are high among elderly women in California. For more details, see Walter, L.C., Lindquist, K., and Covinsky, K.E. (2004, May). "Relationship between health status and use of screening mammography and Papanicolaou smears among women older than 70 years of age." (AHRQ grant K02 HS00006). Annals of Internal Medicine 140, pp. 681-688.

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