The study was performed to assess the role of DBT as an addition to routine DM as it is a promising and emerging tool for breast cancer screening and diagnosis. Supplemental US was used to analyze the increased accuracy of this modality for lesion characterization.
A total of 313 masses were picked up on 2D mammography alone while 2D and 3D mammography combined picked up 361 lesions thus showing that 3D mammography improves lesion visualization (Fig. 1). A total of 77 circumscribed lesions were picked up on 2D mammography while 123 circumscribed lesions were picked up on 3D mammography. This finding coincides with that of Nakashima et al. [14] who showed superior overall visibility of circumscribed masses on DBT images as compared to 2D mammograms in 59 cases. Lesion conspicuity was improved with DBT with fewer lesions having obscured (27.4%) and indistinct margins (8.6%) as compared to DM which showed 29.7% obscured and 17.9% indistinct margins. The detection of spiculated margins also increased to 24.7% with DBT as compared to 22.7% with DM alone (Figs. 2, 3). This is consistent with the findings of Chan et al. [15] who showed significantly higher conspicuity of lesions on DBT than in DM.
The reason for improved visibility of lesions on DBT was that the overlapping tissue in DM was largely removed by DBT. Lesion characteristics such as the shape and margin, therefore, became more visible. The improved conspicuity and margin characterization contributed to the improved assessment of the degrees of suspicion.
DBT has shown higher sensitivity in detecting architectural distortion as compared to DM. Studies by Dibble et al. [16] had higher confidence and higher agreement with DBT as compared to DM in detecting architectural distortion in screening mammograms. Rafferty et al. [17] also showed that digital mammography plus tomosynthesis demonstrated superior diagnostic accuracy in identifying architectural distortion. In our study, we did not observe a significant difference with the addition of DBT possibly because our study had very limited screening cases like Dibbles and Rafferty (Fig. 4). We also had a smaller sample size as compared to the above studies.
The role of DBT in detecting microcalcifications has been studied and lesions that have microcalcifications as their main feature may not be seen at DBT occasionally [18]. In our study, DBT did not show superior performance for the detection of microcalcifications and rather showed no significant difference in identifying them as compared to DM alone. A reason for this could be that we were analyzing DBT images after viewing DM images hence a potential bias could have formed and only the microcalcifications viewed on DM were confirmed on DBT. Studies by Li et al. [19] and Kopans et al. [20] have also demonstrated that DBT enabled the detection and characterization of microcalcifications with no significant differences from DM, similar to ours.
The combination of DBT with DM led to better BIRADS characterization with fewer lesions being characterized as BIRADS 0 (3 as compared to 6 on DM alone), and BIRADS 4 lesions being upgraded to a higher category with 5.6% BIRADS 5 lesions being detected on DM + DBT as compared to 4.3% being detected on DM alone.
For DM alone, the sensitivity was 87.8%, specificity was 60%, PPV was 81.3%, NPV was 61.1% with a diagnostic accuracy of 81.1%. For DM with DBT the sensitivity was 92%, specificity was 56.5%, PPV was 89%, NPV was 65% with a diagnostic accuracy of 84.8%. Our study showed higher sensitivity, NPV and diagnostic accuracy of combined DBT with DM as compared to DM alone. This is similar to the findings of Lei et al. [21] who in their meta-analysis of 7 studies found higher pooled sensitivity with DM in combination with DBT as compared to DM alone, similar to our study. Gilbert et al. [9] in the TOMMY trial also reported an increase in sensitivity with 2D + DBT where the dominant radiological feature was a mass, with 89% sensitivity for DM and 92% for DM + DBT, in concordance with our findings. Similar findings were also reported by Rafferty et al. [17] and Asbeutah et al. [22] who had higher sensitivity, NPV, PPV and diagnostic accuracy with DM + DBT. Our study shows higher diagnostic accuracy with combined DBT and DM, correlating with the findings of Mariscotti et al. [23] who also demonstrated higher accuracy with the addition of DBT to DM.
However, this is in slight contrast with the OSLO trial conducted by Skaane et al. [5] in 2019, and study by Ohashi et al. [24] who reported significantly higher sensitivities with the addition of DBT (54.1% for DM vs 70.4 for DM + DBT% and 61% for DM vs 83% for DM + DBT, respectively). Our modest improvement in sensitivity could be explained by the fact that ours is a tertiary care cancer hospital where most of the referred women were already at an advanced stage in their cancer development, i.e. presenting with BIRAD 4 and 5 category masses in contrast with the OSLO trial which was a screening trial. Since most malignant masses may be demonstrable on DM alone, we may have underestimated the contribution of DBT, serving as a potential limitation in our study. The above studies also operated with very large sample sizes as compared to our modest sample size of 1228 breasts. This could be a potential factor affecting the results.
Ultrasonography is complementary to mammography in patients with palpable abnormalities; its superiority over mammography is in being able to show lesions obscured by dense breast tissue and in characterizing palpable lesions that are mammographically visible or occult. Ultrasound is instrumental in determining solid vs. cystic nature of a lesion, vascularity of a lesion (Fig. 5) and duct changes which have been documented in studies by Jackson [25] and Chao et al. [26].
In our study, 413 masses were detected on USG which were higher than the 313 picked up on DM alone and 361 detected on DM with DBT. A total of 119 cases in our study showed duct changes on US which could not be assessed on mammography alone and 158 cases showed increased vascularity (either internal or rim or a combination of both) on US which could, again, not be demonstrated on mammography alone. Posterior features as an adjunctive finding in the diagnosis of breast lesions could only be determined with US. In total, 40 intramammary lymph nodes were diagnosed with US while only 20 and 14 were diagnosed with DBT + DM and DM alone, respectively. A total of 11 cases on ultrasound showed post-surgical fluid collection and simple or clustered microcysts could only be detected on US.
Few benign appearing lesions on mammography (round with circumscribed margins) demonstrated solid nature on US with internal vascularity thus highlighting the role of US in characterization of the internal contents of benign appearing masses.
With the use of US, no breast was given a BIRADS 0 assessment as compared to 6 on DM and 3 on DBT, reducing the number of non-diagnostic cases. There was a reshuffling of BIRADS with a higher number of lesions being assigned BIRADS 3, 4a, 4c and 5 categories as compared to DM alone or DM + DBT. The number of BIRADS 1 and 4b category was lesser with the use of US than with mammography alone, being re-assigned to a higher category.
The combination of all the modalities together yielded a higher sensitivity of 96.3% as compared to DM alone or DM + DBT. We also observed a significantly higher NPV of 82% with all the modalities combined. Higher diagnostic accuracy of 85.1% was observed with all three modalities combined but specificity and PPV were slightly lower than with DM and DM + DBT. This is in concordance with the findings of Mariscotti et al. [23] who found overall accuracy rates of 86.9% using DM alone, 90% with DM + DBT and 93.7% with the combined usage of all three modalities in conjunction with each other. They also reported higher sensitivity for DM + DBT + US of 95–98.9% as compared to DM alone (80.5–89.2%), similar to ours.
Higher diagnostic accuracy and higher sensitivity of the combination of mammography and ultrasound in contrast with mammography alone was also demonstrated by Berg et al. [27]. The combination had a higher sensitivity of 77.5% as compared to mammography alone which had a sensitivity of 50%. They found a significantly higher diagnostic accuracy of 91% for mammography plus ultrasound combined in comparison to mammography alone which was 78%.
Ying et al. [28] also reported higher sensitivity of 99.19% and higher NPV of 99.37% with combined US and Mammography. Buchberger et al. [29] also had higher sensitivity of 90.6% with combined MM + USG as compared to 78.5% with mammography alone.
Our study had a few limitations: As compared to western screening studies, our study had a relatively small sample size. Awareness about screening for breast cancer is, unfortunately, still lacking in our nation and thus we had very few cases that came for screening. Since ours is a tertiary care cancer hospital, our data set comprised of patients who had advanced stages of malignancies that could be detected on DM alone, thus we might have underestimated the importance of DBT to a certain extent. Pathological specimens of 77 cases were not available as some of these women were lost to follow up while others did not get treated further in our institute.