Ultrasonography is an important technique to screen for breast lesions. BI-RADS has been developed to describe the characteristics of these lesions in order to categorize them according to the likelihood of malignancy. According to the 2013 version of the BI-RADS classification, BI-RADS 4 is further subdivided into BI-RADS 4a, 4b, and 4c. BI-RADS 4a is assessed as a possible benign tumor (3% − 10% likelihood of malignancy), in which case an aspiration biopsy or a short-interval follow-up is recommended. BI-RADS 4b is assessed as a possible malignant tumor (11% − 50% likelihood of malignancy), in which case a biopsy should be performed. BI-RADS 4c indicates a high malignancy rate (51% − 94% likelihood of malignancy), for which a biopsy or surgery is indicated 8,9. However, all nodules classified into the BI-RADS 4 category, without further division into 4a, 4b, and 4c subgroups, are predicted to have a 3–94% malignancy rate. Not only does such a wide range pose the risk of unnecessary biopsies or surgeries, but also involves great variability in how breast nodules are treated 10,11. In breast cancer, the size of nodules is an important prognostic index. The largest diameter of early breast cancer is usually ≤ 20 mm, of which the nodules with a diameter ≤ 10 mm are referred to as microcarcinoma. Not only the size of the nodule, however, determines an accurate diagnosis. The performance of BI-RADS in diagnosing early breast cancer may be compromised by atypical image features specific to early breast cancer, overlapping ultrasound images 12,13. Based on the features of benign and malignant breast nodules, S-Detect processed specific parameters from ultrasound images to accurately identify abnormalities. Then S-Detect automatically identified the lesion as probably benign or probably malignant, by analyzing the size, shape, boundary, retrotumoral echo of the given breast nodule Automation provided by S-Detect eliminates the bias arising from subjective physicians’ assessments 14 and has shown higher performance in diagnosing breast nodules, as proven by other studies 15. Nevertheless, studies on S-detect as an additional technique improving the diagnostic performance of BI-RADS 4 breast nodules with different sizes is need to be further studied.
Herein, we found that Co-Detect (BI-RADS/S-Detect in combination) could have higher diagnostic performance and that this performance varied with the size of nodules. Specifically, for breast nodules ≤ 20 mm, SE, ACC, NPV, and AUC were improved in the Co-Detect group, with a statistically significant difference (P < 0.05). For breast nodules ≤ 20 mm, SE, SP, ACC, PPV, and NPV were improved in the Co-Detect group, but the difference was not statistically significant (P < 0.05). We indicated that the diagnostic performance of Co-Detect was associated with the size of nodules, especially with the size ≤ 20 mm. The possible reasons include small lesions in early breast cancer, a weak interstitial response, a loose arrangement of fibrous tissues, fewer new blood vessels, and tumor cells not infiltrating the periphery of the lesion. Thus, it is difficult to differentiate between benign and malignant nodules with conventional ultrasound imaging, especially for physicians with insufficient experience. A 53-year-old female patient included in this study had a 5.4 × 6.5 mm nodule in her right breast (Fig. 2). The ultrasound scan showed a clear boundary, irregular shape, uniform echo, and the longitudinal/transverse ratio > 1. The nodule was classified as BI-RADS 4a by two ultrasonographers. The classification results based on longitudinal and transverse sections obtained with S-Detect were both possibly malignant. Therefore, this nodule was finally diagnosed as a malignant tumor which proved to be an invasive lobular carcinoma, as confirmed by histopathology. Another 39-year-old female patient had an 11.0 x 8.2 mm nodule in her left breast (Fig. 3). The ultrasound scan showed a clear boundary, irregular shape, uniform echo, and antiparallel orientation. The nodule was also classified as BI-RADS 4a by two ultrasonographers. The classification results based on longitudinal and transverse sections obtained with S-Detect were both possibly benign. Thus, this nodule was finally diagnosed as a benign tumor which proved to be an intraductal papilloma by histology. The results obtained with S-Detect became reliable medical recommendations to clinicians on diagnosing benign and malignant nodules from the BI-RADS 4 category, especially breast nodules ≤ 20mm. According to the BI-RADS, S-Detect standardly evaluated and differentiated benign from malignant breast nodules. S-Detect provided a comprehensive practical reference and avoided a bias resulting from a subjective assessment of the physician, thus improving the diagnostic efficiency for breast nodules and playing a more effective role in assisting diagnosis 16,17,18. For breast nodules > 20 mm, due to the long growth time, some nodules have typical malignant characteristics, including internal liquefaction and calcification. Hence it is easy to differentiate benign breast nodules larger than 20 mm from malignant lesions by conventional ultrasound. Thus, the role of S-Detect in enhancing diagnostic efficacy for breast nodules larger than 20 mm was less significant.
Compared with the studies using S-Detect to diagnose breast nodules, we diagnosed BI-RADS 4 nodules of different sizes. SE, SP, ACC, PPV, NPV, and AUC were used to assess the diagnostic value of S-Detect for BI-RADS 4 nodules of different sizes 19,20,21. We found that S-Detect could use the difference in nodule size to differentiate benign from malignant BI-RADS 4 breast nodules. The diagnostic coincidence rate of S-Detect was considerably higher than that of conventional ultrasound diagnosis, providing comprehensive guidance in clinical practice. A study has revealed that the use of S-Detect alone or overreliance on S-Detect technology can cause missed diagnoses and misdiagnoses in clinical practice. At present, S-Detect is recommended only as an auxiliary diagnostic tool, rather than as a single or definitive diagnostic method 22,23,24.
Although S-Detect had a high diagnostic efficacy for BI-RADS 4 breast nodules, there were still certain limitations to the study: (1) This was a single-center study and there was only one type of pathological result examined. Most of the malignant nodules were invasive ductal carcinoma, and most of the benign nodules were fibroadenosis with or without fibroadenoma, with other pathological types being rare; (2) Breast nodules were three-dimensional, while the diagnosis made with S-Detect technology was based mainly on analyzing static images of nodules obtained from the maximum section and vertical section. Therefore, there was a degree of subjectivity in the assessment, although sonographers analyzed the most representative section of the lesion. In subsequent studies, the sample size should be increased for greater validation of the results.