## 1 Introduction  
Breast cancer among women, although one of the most common cancers, can have a good prognosis if detected and treated promptly [1]. For these reasons, it is necessary to continuously improve and adjust diagnostic methods in order to increase patient receptivity. Attention must be focused on improving noninvasive diagnostic methods in order to minimize unnecessary surgery.  
Mammography screening was proven to detect cancer at an early stage with an estimated relative reduction of mortality of 15% in women aged 50 and over [2]. Although effective, mammography has its limitations [3]. Several factors such as dense breasts and patient age under 40 limit its applicability [4; 5; 6].  
Breast ultrasonography as a complementary diagnostic method allows circumventing the age and breast density limitations of mammography, as well as being able to differentiate solid from cystic lesions and evaluate palpable breast lesions not visible on mammography and being suitable for pregnant patients [7; 8; 9; 10].  
Subsequently, by introducing high-frequency transducers, ultrasonography allows the differentiation of malignant from benign breast masses [8; 11; 12], leading to it being a candidate for a first-choice diagnostic method in breast cancer screening [13]. As a simple, noninvasive, nonirradiating and painless technique, it can be easily performed routinely in order to solve the patient addressability issue.  
Real-time elastography is a recent imaging technique used complementarily to conventional US, resulting in increased diagnostic accuracy [8; 14; 15].  
Sonoelastography screening for breast cancer is a valuable diagnostic tool, leading to a decrease in unnecessary biopsies [16; 17]. Recent studies show a 9.4% unnecessary biopsy rate if breast sonoelastography is implemented as the screening method [16]. Despite this, breast cancer screening through ultrasonography can still be improved to reduce the number of unneeded biopsies [18; 19; 20], which is required in order to avoid causing the patients additional discomfort and emotional distress [21; 22].  
The American College of Radiology (ACR) developed a common and reproducible way of breast ultrasound interpretation. Breast lesions are evaluated based on well-defined criteria including the shape, boundary, echo pattern, orientation, margin and posterior acoustic features and classified into BIRADS (Breast Imaging Reporting and Data System) categories 1 to 5 [23].  
Current recommendations by the EFSUMB and WFUMB guidelines are to downgrade the BIRADS scores 4A and below in cases with low stiffness but not in cases with a BIRADS score of 4B or higher [24].  
One contribution of our study was the introduction of two new risk-stratification reporting systems (BIRADS TM and BIRADS worst case) combining both qualitative and semiquantitative elastography methods with conventional breast ultrasound, allowing both downgrading and upgrading the conventional BIRADS US score, a novel approach not yet identified in the current literature.  
Another contribution with regards to the current available literature on the subject was the evaluation of a significantly higher number of solid breast nodules. Comparable studies have analyzed breast nodule sample sizes ranging from 99 to 200 [18; 19; 25]. We analyzed 1405 solid nodules, of which 93 were later confirmed to be malignant.  
The current study is a retrospective study, evaluating the best risk-stratification reporting system using any combination of conventional US, doppler evaluation and strain elastography (both qualitative and semiquantitative techniques) through multiple algorithms for the risk reassessment of solid breast nodules in order to identify the optimal threshold for malignancy.