For diagnostic mammography performed to evaluate an abnormal screening result, facilities serving vulnerable women had similar interpretive performance to facilities serving non-vulnerable women. Only facilities serving limited income women, one of the four categories of vulnerable women, had significantly higher false positive rates relative to those serving non-vulnerable income populations. In contrast, for the interpretation of diagnostic mammography to evaluate a symptomatic breast problem, facilities serving a greater proportion of vulnerable women were more likely to recommend a biopsy or surgical consultation among women not subsequently diagnosed with breast cancer compared to facilities that did not serve vulnerable women. We did not find associated differences between facilities in the sensitivity or cancer detection rates. The lack of difference in the sensitivity of diagnostic mammography to evaluate an abnormal screening result or breast problem for vulnerable and non-vulnerable populations is reassuring and indicates that the characteristics of the facilities where women go does not appear to influence cancer detection among those with cancer. However, the higher false positive rates at facilities serving vulnerable women suggest these women may be more likely to receive breast biopsies when they don’t have cancer.
Our findings for diagnostic mammography differ from our prior study for screening mammography. (9
) The previous study, which also used BCSC data (1998–2004), found radiologists at facilities serving women with lower educational attainment, racial/ethnic minorities, limited income, and rural residences tended to have lower false positive rates (higher specificity). These contradictory results suggest factors driving mammography interpretive performance could differ between screening and diagnostic mammography. For one, differences in cancer prevalence among women undergoing screening and diagnostic mammography may influence radiologists’ perception of cancer risk and therefore the likelihood that they would recommend women return for further testing. In settings where availability of diagnostic imaging is limited and where cancer prevalence is low (i.e. low-risk screening population), radiologists may be less likely to recall women for diagnostic mammography. In contrast, in settings where the cancer prevalence is higher, as occurs with diagnostic mammography, radiologists may be concerned that women may not return for follow up evaluation, and therefore may be more likely to recommend a biopsy as opposed to short-interval follow-up, additional diagnostic imaging, or clinical follow-up. To clarify, while radiologists are unlikely to know the likelihood of a given woman’s follow-up or cancer risk, their practice patterns are likely to be influenced by the overall follow-up rates and cancer prevalence of the population of women evaluated at the mammography facility. Follow-up rates after screening mammography for women with lower educational attainment, racial/ethnic minorities, and women with limited income are lower than for other women.(22
) Similar concerns may exist for diagnostic mammography. In addition, because the unadjusted cancer rates (representative of cancer prevalence) at facilities serving vulnerable women are higher, radiologists may have a greater concern that these women are more likely to have cancer and therefore may recommend more biopsies or surgical follow-up in symptomatic woman attending these facilities. This increased likelihood to recommend biopsy or surgical follow-up could explain the higher false positive rates at these facilities.
Availability of screening and diagnostic mammography may differ across facilities. Radiologists at these facilities may have different experience in interpreting diagnostic and screening mammography. Facilities serving vulnerable populations may tend proportionately to perform more screening than diagnostic mammography, and therefore, have lower false-positive rates for screening mammography and higher false-positive rates for diagnostic mammography. (23
) Facilities serving limited income women were the only type of facility serving vulnerable women that demonstrated higher false positive rates for diagnostic mammography to evaluate an abnormal screening result. These facilities may have specific resource limitations, such as lack of breast ultrasound. (24
) We did not have these data available to us for this analysis.
There are several important strengths and limitations to the study. We used a diverse cohort of many facilities across seven sites in the United States representative of community practice and evaluated the impact that the vulnerability of a population which a facility serves has on the accuracy of diagnostic interpretations using multiple characterizations of vulnerable women. While the higher false positive rates seen at facilities serving vulnerable women may lead to more biopsies in women who do not ultimately receive a cancer diagnosis, our study could not determine this specifically because detailed utilization data to determine whether referral for biopsy truly equated to receiving a biopsy were not available for all facilities. Lower biopsy rates could delay cancer diagnoses, and in effect, artificially raise the false positive rates in vulnerable women. It is possible that vulnerable women may be less likely to receive follow up, which could artificially increase false positive rates at facilities serving vulnerable women if some of these women lost-to-follow-up truly had cancer. To address this concern, we conducted a sensitivity analysis that extended the follow-up time for diagnosis from 1 to 2 years and did not find any difference in our findings.
We selected several measures of vulnerability to help identify facilities serving vulnerable women; however other definitions could be considered with different thresholds. Our study was limited to mammograms with BI-RADS breast density reported because breast density is a known confounder of interpretive performance. We found no substantial differences in sensitivity or false positive rates between included facilities and those excluded due to missing breast density values; however, the cancer detection rate was somewhat lower among excluded facilities. We note, though, that a number of these excluded facilities were from large urban centers which, consistent with our main analysis results, would be estimated to have lower cancer detection rates than facilities serving more rural populations.
Finally, this analysis evaluated the impact of differences in mammography facility-level characteristics on diagnostic performance at the level of a woman’s mammography exam. We did not control for radiologists’ experience, equipment, or practice patterns, which can contribute to diagnostic mammography interpretive performance.(2
) Our analysis, however, has significance from the perspective of a woman choosing to undergo a mammography at a given facility. While women may be able to select where her mammography is performed, she did not have the ability to select who will interpret her mammogram at a particular facility. The experience of the collective group of radiologists and the equipment or the practice patterns at a facility were unmodifiable facility characteristics from the perspective of the woman; therefore, we did not adjust for them.
In conclusion, for diagnostic mammography indicated for evaluation of a symptomatic breast problem, facilities serving vulnerable populations, in general, had higher rates of biopsy or surgical consultation recommendations in women who did not have a subsequent diagnosis of cancer than did at facilities serving fewer vulnerable women; however, significant differences in sensitivity were not observed between such facilities. Facilities serving limited income women undergoing diagnostic mammography to evaluate an abnormal screening result additionally demonstrated greater rates of biopsy and surgical consultation referral among women who did not have a subsequent diagnosis of cancer than did facilities serving non-limited income women. Research should be conducted to determine the appropriate thresholds for referring women to biopsy in different clinical situations for optimal cancer yield per biopsy. As accuracy may differ between screening and diagnostic mammography, both should be assessed when evaluating the quality of mammography at facilities. Future research should consider evaluating facility characteristics such as availability of ultrasound and other diagnostic resources to better understand potential modifiers of diagnostic accuracy.