A total of 241,222 screening mammography exams, performed on 201,470 unique women, were interpreted as abnormal with recommendations for additional evaluation. Of these, 3,624 (1.5%) mammograms were of women who were underweight at the time of the mammogram; 109,738 (45.5%) were of normal-weight women; 73,477 (30.5%) were of overweight women; and 54,383 (22.5%) were of obese women (14.2% Class I, 5.3% Class II, and 3.0% Class III). The mean age of the entire sample was 55 years, with an interquartile range of 46–62 years. Approximately 77% were White, 12%, Hispanic, 4% Asian, and 2% Black.
reports woman-level characteristics, reported at the time of screening mammography, by BMI category. Underweight women tended to be older (age >70 years) and Asian. Obese women tended to be middle-aged (50–59 years), Black, have less than a college education, and have almost entirely fatty breasts. Obese women tended to report no prior mammograms or a longer time elapsed since their last mammogram.
Woman-level characteristics at the time of the index screening mammogram.* Values are column percentages of non-missing observations, within body mass index (BMI) categories
A total of 262,867 distinct recommendations for follow-up resulted from the 241,222 abnormal screening mammograms (). Of the recommendations, 27,057 (10.3%) were for short-interval follow-up; 201,204 (76.5%) for additional imaging; and 34,606 (13.2%) for biopsy or surgical consultation. Of the 241,222 mammograms, 21,645 (9.0%) had an initial recommendation for short-interval follow-up or additional imaging as well as a final recommendation for biopsy or surgical consultation after the workup was completed. Overweight and obese women received more recommendations for short-interval follow-up (14.3% and 16.0% for Class II and Class III obese women, respectively; ) than underweight or normal-weight women (8.9% and 8.7%, respectively), whereas underweight and normal-weight women received more recommendations for additional imaging (76.0% and 78.7%, compared to 70.8% and 69.1% for Class II and Class III obese women, respectively).
Follow-up after abnormal screening mammograms by follow-up recommendation and self-reported body mass index (BMI)
Relationships between BMI and obtaining follow-up for an abnormal mammogram
Overall, 198,456 of the 262,867 recommendations (75.5%) had a recorded follow-up in the BCSC system. Among short-interval follow-up recommendations, the overall percentage with a recorded follow-up was 56.2%; among the additional imaging and biopsy/surgical consultation recommendations, the percentage was higher, at 78.0% and 76.0%, respectively (). Within each of the recommendations, the percentage with observed follow-up did not vary substantially by BMI category, providing little evidence of an unadjusted association. For additional imaging, the percentage increased from 76.4% for underweight women to 81.1% for Class II obese women. Similarly, there was little variability across the BMI groups for either the median or mean follow-up times.
In logistic regression analyses, BMI had a statistically significant effect on recorded follow-up among women with a recommendation for short-interval follow-up (p=0.04; ). Compared to normal-weight women, women in the overweight and obese groups had equal or slightly better adjusted odds of recorded follow-up within 270 days; the estimated odds ratio (OR) varied between 1.02 and 1.10, although no consistent pattern was observed. Compared to normal-weight women, underweight women were estimated to have slightly lower odds of recorded follow-up (OR 0.81; 95% CI 0.65, 1.01). further explores the reduced odds among lower-weight women by presenting results based on a model in which BMI was treated as a continuous exposure. We found that the odds of recorded follow-up increase fairly linearly until a BMI of approximately 30 and plateau thereafter. The association persisted in the fully adjusted model (p=0.025; ). Findings were similar when we used our secondary outcome of recorded receipt of the exact procedure recommended, with women in the overweight and obese groups having slightly higher odds of a recorded follow-up after a short-interval follow-up recommendation (p<0.01 for both adjustment models; data not shown).
The relationship of women’s body mass index (BMI) to recorded receipt of follow-up within 270 days after abnormal screening mammogram recommendations
Figure 1 Estimated adjusted odds ratio (OR) association between body mass index (BMI) and recorded receipt of follow-up within 270 days of an abnormal screening mammogram with a recommendation for short-interval follow-up. Estimates are from a logistic regression (more ...)
For women with a recommendation for additional imaging, higher BMI was statistically significantly associated with increased odds of recorded follow-up within 270 days based on our primary model (p=0.01; ); estimated OR varied between 1.03 and 1.09 for overweight and obese women compared to normal-weight women. However, this association did not persist in a fully adjusted model (p=0.44; ), nor when we used our secondary outcome of recorded receipt of the exact procedure recommended (data not shown). For women who received a recommendation for biopsy or surgical consultation, there was no evidence of an association between BMI and any recorded follow-up () or receipt of biopsy (data not shown).
BMI and time to recorded follow-up
Among short-interval follow-up recommendations, the mean number of days to follow-up for women in the normal weight range was 170 days (standard deviation (SD) 60 days); for overweight and obese women, the mean time was longer by 4–12 days (). Median times to recorded follow-up were 183–185 days among all groups. While linear regression analyses indicate a statistically significant adjusted association between BMI and time to recorded follow-up (p<0.001 for both adjustment models; ), differences across the BMI groups were small relative to the overall mean of 173 days. For example, compared to normal-weight women, the mean time to follow-up was estimated to be 6 days longer for the Class I obesity group (95% confidence interval (CI) 4–6) and 10 days longer for the Class III obesity group (95% CI 6–14). Results did not change based on the secondary outcome of recorded receipt of the exact procedure recommended (data not shown).
The relationship of body mass index (BMI) to the timing of observed follow-up for abnormal screening mammogram recommendations
Among additional imaging recommendations, the mean number of days varied only slightly across BMI categories (range 23–25 days); the median was 13 days for each category (). Based on adjusted analyses, obese women (Classes I–III) were estimated to have a mean time to follow-up that was 2–3 days longer than women in the normal weight range (p<0.001 for both adjustment models; ). Again, results did not change when the outcome was restricted to receipt of recommended examination.
Finally, among recommendations for biopsy or surgical consultation, the mean time to obtaining any follow-up ranged from 33 to 35 days (). Based on adjusted analyses, we found no evidence of an effect of BMI on time for any recorded follow-up after a recommendation for biopsy or surgical consultation (). Results did not change based on the secondary outcome, which was restricted to receipt of biopsy (data not shown).
BMI and timely follow-up
To further assess timeliness of follow-up, we performed an additional analysis to examine the effect of BMI on the likelihood of obtaining a recorded follow-up within 60 days of recommendations for additional imaging or biopsy/surgical consultation. Results were non-significant for our primary model when we examined outcomes of receipt of either any follow-up examination (p=0.53) or the specified procedure after a request for additional imaging (p=0.12). However, the fully adjusted model that, in addition to study site, age, education, and race, adjusted for breast density, family history of breast cancer, hormone use, and screening interval, showed consistent evidence of an effect of BMI across all BMI groups (any follow-up outcome p< 0.01; specified examination only p< 0.001). Among the obese groups, the actual reduction in odds of recorded follow-up within 60 days was small; no OR for any BMI group was < 0.93. Thus, only in our fully adjusted models, higher-weight women were 3–8% less likely to obtain follow-up examinations within 60 days after a recommendation for additional imaging. There were no significant differences by BMI in the odds of follow-up within 60 days after a recommendation for biopsy or surgical consultation for any follow-up procedure (p=0.53, fully adjusted p=0.62) or for biopsy specifically (p=0.67, fully adjusted p=0.71).
Interactions between BMI and race/ethnicity
Effect modification by race/ethnicity was explored by using the categories presented in , with “White, non-Hispanic” taken to be the referent group. Neither of our logistic regression analyses of receipt of follow-up within 270 days provided evidence of a significant interaction between race/ethnicity and BMI for any of the three recommendation types (data not shown). For linear regression analyses of time to follow-up, a statistically significant interaction was found between race and BMI among additional imaging recommendations (p=0.03 for both adjustment models; data not shown). However, as with the results from the main analyses, race-specific differences across BMI groups were slight. The only BMI category with a consistent difference in mean time to follow-up across race/ethnicity was the Class III obese group: three days (95% CI 2–4) for Whites, eight days (95% CI 0–15) for Blacks, and five days (95% CI 1–10) for Hispanics.