The percentage of false-positive mammography results observed in our study in São Paulo (52.8%) was significantly higher than the rates reported in studies from high-income countries such as the United States and Germany, which ranged from 12–20% [4, 5]. These discrepancies may be partly attributed by differing criteria used to define false-positive results. For instance, the study in the United States focused solely on false-positive rates from digital mammography screening, which is more accurate in women under the age of 50, women with dense breasts, and premenopausal or perimenopausal women [23]. In São Paulo, the widespread use of digital mammography has only recently become common. Nevertheless, the high rate of false-positives observed in our study indicates a significant barrier to the effectiveness of the breast screening program in the state. It is therefore crucial to understand the factors contributing to false-positive mammography results and to develop strategies to address this issue.
In this study, we investigated the factors contributing to false-positive results in mammography screening, recognizing that evaluating these factors is essential for assessing the extent of breast cancer overdiagnosis in a given population [24, 25]. Understanding these causes can help refine screening protocols, improve diagnostic accuracy, reduce anxiety among women undergoing screening, and minimize unnecessary follow-ups.
This was the first study conducted in Brazil using population data to associate false-positive mammogram results with both screened women-related factors and breast lesion-related factors. Our results indicate that women under 50 years, those using hormone therapy, and those with dense breasts, as well as lesions with defined edges smaller than 10 mm and calcifications, were the main factors affecting mammography accuracy.
False-positive mammogram results have been associated with age, hormone therapy, familial history of cancer, and breast density in previous studies [5, 24, 25]. The new recommendation by the US Preventive Services Task Force to lower the starting age for mammographic screening from 50 to 40 years is under debate [26]. The age for breast cancer screening has also been a subject of controversy in Brazil. The Brazilian Ministry of Health recommends screening mammograms every two years for women aged 50 to 69 [16], while the Brazilian Society of Mastology also advocate mammograms for women aged 40 to 49 [27]. As our study detected a higher proportion of false-positive results among women under 50, lowering the starting age for mammographic screening could reduce accuracy and increase the rate of overdiagnosis, potentially negatively impacting women's emotional health [28–30].
Reduced mammography accuracy has also been found in women over 50 years of age who are undergoing hormone therapy, as they tend to have a higher proportion of dense breast tissue compared to non-users [31–33]. A meta-analysis suggested that age may influence the association between hormone therapy use and mammography sensitivity and specificity [34]. Our data showed an increase in false-positives among women using hormones, regardless of age. Additionally, our results revealed a higher percentage of false-positives among women with dense or predominantly dense breasts. However, more studies are needed to adequately evaluate the impact of the type, duration, and doses of hormonal therapy on false-positive mammogram results and their relationship with the woman's age.
Familial history of cancer is a variable to be considered in the context of an organized breast cancer screening program, although the hereditary factor in the causality of breast cancer accounts for less than 10% [35]. Nelson et al. [5] suggested that false-positive mammography results are relatively common in younger women with a history of cancer in their family. In our study, we did not find an association between false-positive mammograms results and familial history of cancer. In fact, an opposite trend was observed.
The detection of breast cancer through mammographic examination depends on aspects related to the lesions. Some characteristics of breast lesions can be easily identified, facilitating diagnosis. On the other hand, other features are subtle, making the diagnosis more challenging. Moreover, some lesions are visible on mammograms, although the images do not match the pathological diagnoses [19–22]. In our study, we found an association between false-positive results and the presence of calcifications in women undergoing to screening mammograms. Microcalcifications have been associated with benign lesions, while large solid lesions are more often associated with malignant ones [22]. Cole et al. [21] found a higher sensitivity for the interpretation of solid masses and a lower sensitivity for the interpretation of calcifications using three image-processing algorithms.
The topographic location of the breast lesion can be a useful factor in evaluating mammography accuracy, as tissue characteristics differ in the upper, lower, medial, or lateral areas of the breast. For example, glandular tissue is concentrated in the upper and outer areas, while the proportion of adipose tissue varies in different areas. This density distribution can affect how abnormalities are detected by mammographic exams. [36, 37]. We did not find significant association between different breast areas and mammography sensitivity. However, it is important to consider that mammography sensitivity can be influenced by the patient's menstrual cycle during the mammogram and the training of professionals responsible for conducting the examination and evaluating the images [38, 39].
We found that women with true-positive mammogram results experienced an average diagnosis period four times longer than the maximum of 30 days established by Brazilian legislation. For women with false-positive mammogram results, the time to diagnosis is even longer. Experiencing a false-positive mammogram actually increases the risk of late-stage diagnosis, as these women are more likely to delay subsequent mammograms [39–41]. Another concern in the state of São Paulo is the high percentage of women with suspicious (BI-RADS 4) or highly suspicious (BI-RADS 5) mammograms who did not undergo biopsies or were lost to follow-up. This highlights the need for an effective information system to monitor women screened for breast cancer within the context of an organized breast cancer screening program.
Some limitations can be pointed out in our study, including the lack of data related to body mass index and the absence of information on the type and duration of hormonal therapy in the SISMAMA database, which could potentially affect the sensitivity of mammography. Furthermore, there is a notably high amount of missing data for skin color, education, lesion topographical site, and lesion edges. However, this did not impede the analysis of these variables.
Analyzing big data in health is essential for evaluating and implementing clinical interventions, as well as for establishing public health policies. Health information systems can provide valuable and reliable data on factors associated with mammogram sensitivity. This information is important for planning and improving breast cancer screening programs by reducing uncertainty in results and shortening diagnostic times.