In a rapidly changing clinical environment, assessment of imaging-based technologies and practices for periodic screening for the early detection of breast cancer is constrained by cost, complexity, and professional resources, particularly concerning supplementary imaging of subgroups constituting a large fraction of the screened population. Relatively high survival rates after detection make it extremely difficult to adequately assess marginal values of proposed approaches either before the technology in question being widely accepted and used or before it becomes largely obsolete. The author discusses several issues related to the assessment process and proposes the use of a surrogate summary measure of performance for this purpose, namely the number of recalled cases for the diagnostic workup of suspicious findings during repeat examinations, per one additional screen detected cancer that is invasive, node-negative, and classified grade 2 or above.
In recent years, there have been a number of new technologies and practices aimed specifically at improving the early detection of breast cancer, particularly for women with dense breast tissue. Several modalities have been discussed for possible use as primary and/or supplementary procedure(s) for screening the general population and large subgroups of women . Although magnetic resonance imaging (MRI) is currently used for screening women at high risk , screening women with dense breast tissue is clearly the focus of many of these new procedures, because these women are considered to be at intermediate risk. These procedures include, but are not limited to, hand-held and/or automated whole breast ultrasound (WBUS) , digital breast tomosynthesis (DBT) , molecular breast imaging (MBI) , cone beam computed tomography (CBCT) , and contrast-enhanced mammography (CEM) . In most instances, when a modality supplements a current practice (or simply the addition of more images or views using one modality), cancer detection improves because the information ascertained from the current and added modality is not totally correlated–namely, only when the information generated by two modalities (or more) is totally (100%) correlated, no diagnostic improvements are expected by using both modalities, other than possible improvements related to multiple observers interpreting the same case (namely, gaining from interobserver variability). Findings by independent observers are rarely 100% correlated with each other, even when the abnormality in question is quite obvious.
In breast cancer screening, new modalities are frequently viewed as supplementary to mammography rather than as replacements . Hence, the cost and often the complexity of these practices are ever increasing. Clearly, this approach is nonsustainable. Clinicians and investigators should focus on assessing the marginal value of these additional procedures, regardless of any other performance measure considerations, such as cost, professional resources, recall rate, and participants’ anxiety.
Several fundamental concepts should be examined before considering the topic of assessing the true value in general, and a marginal value in particular. First, it is always possible to successfully compete with (or “beat”) poorly performing current (or reference) practices . For example, it would clearly be easier to demonstrate an improvement in cancer detection when supplementing screen film mammography with WBUS in women with dense breasts than when supplementing full field digital mammography (FFDM) based screening. However, because FFDM based screening remains a “less than perfect” procedure, particularly in women with dense breasts, supplementing FFDM based screening with any of the proposed approaches (e.g., WBUS, DBT, MBI, CEM or CBCT) would likely result in detecting additional cancers. The question is always at what cost?
Second, when considering adding new modalities/procedures to current practices for subgroups constituting a large fraction of the screened population (e.g., women with breast density 3 and 4 based on Breast Imaging Reporting and Data System [BIRADS], constituting between 40%–50% of the female population between the ages of 40 and 69), practical/operational issues and financial issues must be carefully considered. In addition, supplementary modalities may increase risk because of additional radiation exposure or repeated injections of contrast media; however, for the purpose of this discussion, I assume that all approaches in question can be considered “safe”.
Third, the slope of incremental performance improvements per unit cost (or additional effort) typically has a negative second derivative resulting in incrementally diminishing returns–namely, adding new procedures to an already accepted group of prior procedures tends to result in a decreasing rate of incremental benefits. At the extreme, when the practice is “perfect” in terms of diagnostic performance, adding supplementary procedures can only add “noise” (and cost); thereby, actually decreasing overall performance without any chance of improving performance.
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