Modeling the impact of a screening blood test on the use of adjunct breast imaging

Historical Origins for the Overestimation of Mammographic Sensitivity

The sensitivity of screening mammography for the early detection of breast cancer has improved over the years due to advances in technology. However, guidelines for screening mammography are often based on the mortality reductions demonstrated in the historic trials, where sensitivity with the first-generation mammography was relatively low. With attempts to establish risk:benefit ratios for population screening, it is important to understand the wide range of sensitivities that have been reported for mammography. 

Original calculations for mammographic sensitivity were often based on studies that included palpable tumors, thus generating inflated numbers not fully applicable to non-palpable tumors. If restricted to asymptomatic screening, sensitivity calculations were often based on the inverse of interval cancers, a relatively inaccurate method since breast cancers missed on mammography can remain undetected clinically for several years. It was not until multi-modality imaging was developed, primarily ultrasound and MRI, where sensitivity determinations could be made in real time by cross-checking outcomes with each modality. From this, it became apparent that there was a strong correlation between breast density levels and sensitivity levels, such that a single number to denote mammographic sensitivity was disingenuous. The increasing awareness that mortality reductions in the historic trials were achieved with a low sensitivity tool has prompted great interest in additional technologic improvements in mammography, as well as multi-modality imaging approaches for women with high density and/or high risk. In order to appreciate the potential benefit of these new approaches, it is helpful to understand the historical basis behind overestimating the sensitivity of screening mammography.

Redefining the sensitivity of screening mammography: A review

From its inception, screening mammography has enjoyed a perceived level of sensitivity that is inconsistent with available evidence. The original data that imparted erroneous beliefs about sensitivity were based on a variety of misleading definitions and approaches, such as the inclusion of palpable tumors, using the inverse of interval cancer rates (often tied to an arbitrary 12 month interval), and quoting prevalence screen sensitivity wherein tumors are larger than those found on incidence screens. This review addresses the background for the overestimation of mammographic sensitivity, and how a major adjustment in our thinking is overdue now that multi-modality imaging allows us to determine real time mammographic sensitivity. Although a single value for mammographic sensitivity is disingenuous, given the wide range based on background density, it is important to realize that a sensitivity gap between belief and reality still exists in the early detection of breast cancer using mammography alone, in spite of technologic advances. Failure to recognize this gap diminishes the acceptance of adjunct methods of breast imaging that greatly complement detection rates.