Synthetic 2D Mammography with 3D Tomosynthesis as Screening Tool: Early Detection and Reduced Recall
Two-dimensionlal (2D) mammography screening programs reduce breast cancer mortality substantially, but they do not depict all cancers early enough to result in a cure. Thus, to detect cancers earlier, the aim has to be to increase the sensitivity and specificity of the diagnostic methods used (Coldman et al. 2007, 2014; Heywang-Köbrunner et al. 2011; The Swedish Organized Screening Evaluation Group 2006; Jonsson et al. 2007; Allgood et al. 2008; Parvinen et al. 2006; Schopper and deWolf 2009; Gabe et al. 2007; Roder et al. 2008; Kopans 2014b). Tomosynthesis (3D) fulfills these criteria and will, in the end, replace standard 2D digital mammography for breast cancer screening (Kopans 2014a). Many of the arguments against 2D mammography screening raised through recent years are based on faulty science (Heywang-Köbrunner et al. 2011; Kopans 2014b). Indeed, there are true disadvantages of 2D mammography screening, such as radiation risks, the risk of a false alarm, interval cancers, and—to a certain point—overdiagnosis (Heywang-Köbrunner et al. 2011). Many of these disadvantages will be markedly reduced due to the emerging widespread use of tomosynthesis. 2D mammography is associated with a small amount of radiation. But the average glandular dose is low, calculated as 4 mGy per breast. The individual dose may differ depending on breast size and compression (Heywang-Köbrunner et al. 2011). According to the literature, tomosynthesis with synthetic 2D views reduces the breast dose by approximately half, which has substantial implications for the future of population screening programs (Svahn et al. 2015). Like every medical test, screening 2D mammography may detect abnormalities that require further evaluation, but will eventually turn out to be benign. Psychologically, such a false-positive alarm causes distress. Meanwhile, many studies have shown that the recall rate of tomosynthesis (2D + 3D) is significantly lower than that in the 2D mammography-alone group, even if the combination 2D + 3D group has additional risk factors (recall rate for 2D, 11.5 %; in the combination 2D + 3D group, 4.2 %) (Destounis et al. 2014). Interval cancers represent a limitation of screening and not a side effect. Screening does not allow us to recognize these cancers at a preclinical stage. They exist, but are 2D mammographically occult and become clinically detectable during the screening interval (Heywang-Köbrunner et al. 2011). Meanwhile, many studies have shown that the use of 2D + 3D in a screening environment results in a significantly higher cancer detection rate and enables the detection of more invasive cancers (Skaane et al. 2013, 2014; Ciatto et al. 2013). It can be accepted that these cancers were occult on the regular 2D mammography screening and later found at a more advanced stage. Improved possibilities of treatment are an important advantage of early detection. It is well known that early detection leads to a reduced number of mastectomies, better cosmetic results in cases of breast conservation, reduced adjuvant chemotherapy, and increased replacement of axillary dissection by sentinel node biopsy (Heywang-Köbrunner et al. 2011). Overdiagnosis of breast cancer in a screening program describes the fact that, in a screened population, more breast cancers are detected than in a comparable unscreened population of the same age and composition. Some of the additional cancers that are detected in the screening group would never have become apparent without screening, and their detection does not contribute to mortality reduction (Heywang-Köbrunner et al. 2011). A quite realistic and very sophisticated calculation was presented by Duffy et al. in 2010 (Duffy et al. 2010). They concluded that the lifesaving effects of mammography screening exceeded the potential harm of overdiagnosis by a factor of 2–2.5. Since some ductal carcinoma in situ (DCIS; even though being a precursor) may not develop into invasive breast cancer during the remaining lifespan of a woman, DCIS must be considered a potential and real source of overdiagnosis or, rather, overtreatment and thus requires special attention. Someone could suggest that the use of 3D would lead to more overdiagnosis/overtreatment and thus in the end to more and more costs. But the contrary is demonstrated by Bonafede et al., who have shown clinical and economic favorability of 3D for breast cancer screening among commercially insured women in the United States (US) (Bonafede et al. 2015).
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