Breast cancer surgery in the era of genetic uncertainty: real-world outcomes in BRCA1/2 pathogenic variants and variants of uncertain significance.

Introduction
Breast cancer remains the most commonly diagnosed malignancy and the leading cause of cancer-related mortality among women worldwide. According to the most recent global estimates from the International Agency for Research on Cancer (IARC), more than 2.3 million new breast cancer cases and approximately 666,000 breast cancer–related deaths were recorded globally in 2022, accounting for nearly one in four cancer diagnoses among women and representing a major public health burden across both high- and low-income countries [1–3].
The burden of breast cancer is also substantial in middle-income countries, including Türkiye, where incidence rates continue to rise and breast cancer remains the most frequently diagnosed cancer among women. GLOBOCAN 2022 data indicate that breast cancer represents the leading cancer diagnosis and the primary cause of cancer-related mortality among Turkish women, with notable variation in age at diagnosis and stage distribution compared with Western populations [4, 5].
Germline pathogenic variants in the BRCA1 and BRCA2 genes confer a markedly increased lifetime risk of breast and ovarian cancer and play a critical role in guiding cancer risk assessment, surveillance strategies, and treatment decisions. Carriers of pathogenic BRCA variants face a lifetime breast cancer risk ranging from 45% to 75%, substantially higher than that of the general population, and often develop cancer at a younger age [6–8]. Consequently, identification of pathogenic BRCA mutations has direct clinical implications, including consideration of intensified screening, risk-reducing surgery, and systemic treatment selection [9].
In contrast, VUS in BRCA1 and BRCA2 represent a major challenge in clinical practice. VUS are frequently detected with the widespread adoption of next-generation sequencing–based multigene testing, yet their pathogenicity cannot be definitively established at the time of detection. Current international guidelines recommend that clinical management decisions should not be based solely on the presence of a VUS; however, accumulating evidence suggests that both patients and clinicians may experience uncertainty that influences surveillance and surgical decision-making despite the absence of clear biological risk [10–12].
Given the growing prevalence of BRCA testing and the increasing detection of VUS, understanding how BRCA variant classification influences real-world clinical decision-making is of critical importance. In this multicenter retrospective study, we aimed to compare clinicopathological characteristics and surgical management patterns between patients carrying pathogenic BRCA1/2 variants and those harboring BRCA VUS, with a particular focus on factors associated with final bilateral mastectomy. Additionally, we sought to explore determinants of surgical decision-making specifically among BRCA VUS carriers, a population in which evidence-based guidance remains limited [13].

Methods

Study design and setting
This was a multicenter, retrospective observational study conducted across three institutions in Türkiye, including two tertiary public hospitals and one private oncology clinic. The study evaluated female patients diagnosed with breast cancer who underwent germline BRCA1 and/or BRCA2 genetic testing as part of routine clinical care. Patients were identified from institutional databases, and clinical, pathological, genetic, and treatment-related data were retrospectively collected.

Study population
Patients with a histologically confirmed diagnosis of breast cancer who were found to carry either pathogenic BRCA1/2 variants or VUS were eligible for inclusion. Germline genetic testing was performed between January 2017 and December 2025, and patients were included if complete information regarding surgical management and key clinicopathological variables was available.
A total of 5667 breast cancer patients were identified across three participating centers.
At the first center, 2991 patients were diagnosed with breast cancer, of whom 139 had abnormal BRCA test results, including 70 pathogenic variants and 69 VUS.
At the second center, 976 breast cancer patients were identified, with 44 patients harboring abnormal BRCA variants, including 27 pathogenic variants and 17 VUS. At the third center, 1700 breast cancer patients were identified, among whom 20 had abnormal BRCA test results, including 10 pathogenic variants and 10 VUS. After exclusion of patients with benign or likely benign variants, male breast cancer, and incomplete surgical data, a total of 203 patients with pathogenic BRCA variants or VUS were included in the final analysis (Fig. 1).

Genetic testing and variant classification
Germline BRCA1 and BRCA2 testing was performed using next-generation sequencing (NGS)–based multigene panels in all centers. Multiplex ligation-dependent probe amplification (MLPA) was additionally used when indicated to detect large genomic rearrangements not reliably captured by sequencing alone.
All BRCA1 and BRCA2 variants included in the study were reviewed in September 2025 according to American College of Medical Genetics and Genomics (ACMG) guideline criteria [10]. Variants identified between 2022 and 2025 underwent formal reclassification as part of this process, while earlier variants were verified using updated database interpretations. Population frequency data were obtained from the Genome Aggregation Database (gnomAD), while clinical interpretations were retrieved from ClinVar, Franklin, and VarSome databases, together with supporting evidence from the current scientific literature. Variants were categorized as pathogenic or VUS based on this reclassification process. During the September 2025 re-evaluation process, VUS carriers were reviewed for potential variant reclassification; however, no variants were reclassified as pathogenic or likely pathogenic.

Clinical and pathological data collection
Demographic and clinicopathological variables collected included age at diagnosis, tumor laterality, clinical tumor size at diagnosis, histological grade, Ki-67 proliferation index, molecular subtype, family history of cancer, and treatment-related variables. Molecular subtypes were defined using immunohistochemical surrogate classification: luminal A (hormone receptor–positive, HER2-negative, Ki-67 < 15%), luminal B (hormone receptor–positive with HER2 positivity or Ki-67 ≥ 15%), HER2-positive (hormone receptor–negative and HER2-positive), and triple-negative (ER-negative, PR-negative, and HER2-negative).
Family history was recorded based on the presence of breast, ovarian, pancreatic, or other malignancies in first- or second-degree relatives, as documented in medical records.

Surgical management and outcome definition
Details regarding initial surgical approach, type of breast surgery, completion mastectomy, and final surgical status were recorded. Bilateral mastectomy was defined as either primary bilateral mastectomy or unilateral mastectomy followed by completion (contralateral prophylactic) mastectomy during follow-up. Patients undergoing unilateral mastectomy without completion mastectomy were classified as having unilateral mastectomy.
The primary surgical outcome of interest was final bilateral mastectomy status, categorized as bilateral versus non-bilateral surgery.

Statistical analysis
Descriptive statistics were used to summarize patient characteristics. Continuous variables were reported as median with interquartile range (IQR) and compared using the Mann–Whitney U test due to non-normal distributions and unequal group sizes. Categorical variables were expressed as number and percentage and compared using Pearson’s chi-square test.
Multivariable binary logistic regression analysis was performed to evaluate factors independently associated with final bilateral mastectomy. In the primary analysis, pathogenic BRCA status versus VUS status was assessed while adjusting for clinically relevant covariates. A separate exploratory regression model was performed among patients with BRCA VUS only, including age at diagnosis, BRCA gene (BRCA1 vs. BRCA2), and luminal versus non-luminal molecular subtype. These exploratory analyses were conducted with particular attention to model parsimony due to the limited number of events. Missing data were handled using complete-case analysis. Descriptive statistics were calculated using available data for each variable, and multivariable regression analyses were performed using cases with complete information for all variables included in the model.
All statistical analyses were performed using IBM SPSS Statistics for Windows, version 26 (IBM Corp., Armonk, NY, USA). A two-sided p value < 0.05 was considered statistically significant.

Results
Baseline clinical, pathological, surgical, and outcome characteristics according to BRCA variant classification are summarized in Table 1. Patients carrying pathogenic BRCA variants were significantly younger at diagnosis compared with those carrying VUS (median 44 vs. 49 years, p < 0.001). Tumor sidedness and initial clinical approach did not differ significantly between groups. Initial tumor size was also comparable between pathogenic and VUS groups.
Tumor grade distribution was similar between groups; however, tumors in the pathogenic BRCA group demonstrated higher proliferative activity, with a significantly higher Ki-67 index compared with the VUS group (median 40% vs. 30%, p = 0.019). Molecular subtype distribution differed significantly, with a higher proportion of triple-negative tumors and a lower proportion of luminal A tumors among pathogenic BRCA carriers (p = 0.001).
A family history of cancer was more frequently observed in the pathogenic BRCA group, particularly involving first-degree relatives with breast cancer (p < 0.001). Surgical management differed between groups: patients with pathogenic BRCA variants were more likely to undergo mastectomy as the initial surgical procedure (p = 0.016), completion mastectomy (p < 0.001), and final bilateral mastectomy (p < 0.001). Prophylactic oophorectomy was also performed more frequently in the pathogenic group (p < 0.001).
At the time of analysis, rates of disease recurrence and death were low and did not differ significantly between pathogenic and VUS groups, supporting the decision not to perform survival analyses.

The distribution of germline BRCA1 and BRCA2 variants according to gene, functional class, biological effect and pathogenicity is summarized in Table 2. The functional classification of variants differed significantly across the four groups (chi-square test, p < 0.001). Truncating loss-of-function variants were predominant among pathogenic mutations in both BRCA1 and BRCA2, whereas non-truncating coding variants were markedly enriched among VUS. Non-coding or other variants were infrequent among pathogenic mutations but were more commonly observed in VUS, particularly in BRCA1.
When variants were classified by biological effect, a significant difference in distribution was also observed across groups (p < 0.001). Frameshift and nonsense mutations were largely confined to pathogenic BRCA1 and BRCA2 variants, whereas missense variants predominated among VUS in both genes. Splice-site and in-frame indel variants were observed less frequently and showed gene- and classification-specific distributions. Other or intronic variants were mainly identified among VUS and were rare among pathogenic mutations.

Multivariable logistic regression analysis was performed to identify factors associated with final bilateral mastectomy (Table 3). After adjustment for age, molecular subtype, Ki-67, tumor grade, and family history of cancer, pathogenic BRCA variant status remained independently associated with final bilateral mastectomy. Patients carrying pathogenic BRCA variants had significantly higher odds of undergoing final bilateral mastectomy compared with those carrying VUS (adjusted OR 10.38, 95% CI 3.98–27.10; p < 0.001).
Increasing age at diagnosis was also independently associated with final bilateral mastectomy (adjusted OR 1.047 per year, 95% CI 1.008–1.088; p = 0.019). Molecular subtype, Ki-67, tumor grade, and family history of cancer were not independently associated with final bilateral mastectomy in the adjusted model (all p > 0.05). The model demonstrated good overall performance, with a Nagelkerke R² of 0.409 and an overall classification accuracy of 77.9%.

Among patients carrying BRCA VUS, clinicopathological characteristics were compared according to final surgery type (Table 4). Final bilateral mastectomy was infrequent in this cohort and was not significantly associated with molecular subtype, luminal versus non-luminal classification, family history of cancer, or BRCA VUS gene (BRCA1 vs. BRCA2) (all p > 0.05). Although numerical differences in the distribution of final surgery type were observed—particularly across molecular subgroups and between BRCA1 and BRCA2 VUS carriers—these differences did not reach statistical significance.
When continuous variables were evaluated, patients who underwent bilateral mastectomy were significantly younger at diagnosis compared with those who underwent non-bilateral surgery (median 43 vs. 49 years, p = 0.043). No significant differences were observed between the two groups with respect to Ki-67 index or initial tumor size (both p > 0.05).

An exploratory multivariable logistic regression analysis was performed among patients with BRCA variants of uncertain significance to evaluate factors associated with final surgery type, with bilateral mastectomy specified as the reference outcome. (Table 5). After adjustment for BRCA VUS gene and molecular subtype, increasing age at diagnosis was independently associated with final surgery type (adjusted OR per year 1.09, 95% CI 1.01–1.17; p = 0.027). BRCA VUS gene (BRCA1 vs. BRCA2) was not independently associated with final surgery type (p = 0.198). Non-luminal molecular subtype showed a numerically lower odds of non-bilateral surgery compared with luminal tumors, although this did not reach statistical significance (adjusted OR 0.30, 95% CI 0.07–1.25; p = 0.099).
The overall model was statistically significant (Omnibus p = 0.026) and explained approximately 20% of the variance in final surgery type (Nagelkerke R² = 0.197).

Discussion
In this multicenter retrospective study, we evaluated the clinicopathological characteristics and surgical management of breast cancer patients carrying pathogenic BRCA1/2 variants or VUS, with a particular focus on the determinants of final bilateral mastectomy. Our findings demonstrate a clear divergence in surgical decision-making between patients with pathogenic BRCA variants and those with VUS, highlighting the clinical uncertainty that continues to surround the management of BRCA VUS carriers.
Consistent with existing evidence, patients with pathogenic BRCA variants in our cohort underwent bilateral mastectomy at substantially higher rates compared with VUS carriers. This observation aligns with established data showing that germline pathogenic BRCA1/2 mutations confer a markedly increased lifetime risk of contralateral breast cancer, for which bilateral mastectomy is often recommended or strongly considered as a risk-reducing strategy [6, 7, 14]. Large observational studies and meta-analyses have demonstrated reduced contralateral breast cancer incidence among BRCA mutation carriers undergoing bilateral mastectomy, supporting its integration into clinical guidelines for appropriately selected patients [15, 16].
In contrast, among patients carrying BRCA VUS, we observed considerable heterogeneity in surgical management. Neither molecular subtype, tumor size, Ki-67 index, family history of cancer, nor BRCA1 versus BRCA2 VUS status showed a statistically significant association with final bilateral mastectomy in univariate analyses. These findings are consistent with prior real-world studies reporting that VUS status alone should not be considered an indication for risk-reducing surgery, given the absence of definitive evidence linking VUS to increased cancer risk [10, 11, 13]. Similarly, a multicenter study published in 2022 reported that the presence of BRCA VUS did not significantly influence therapeutic or prophylactic surgical decision-making in breast cancer patients [17]. Nevertheless, several reports have described substantial variation in clinical practice, with some patients with VUS undergoing aggressive surgical interventions comparable to those offered to pathogenic variant carriers [18, 19].
Notably, in our VUS-only cohort, younger age at diagnosis emerged as the sole independent factor associated with final surgery type in exploratory multivariable analysis. This observation is concordant with previous real-world data suggesting that younger patients may be more inclined toward bilateral mastectomy, potentially reflecting heightened risk perception, longer anticipated lifespan, or greater anxiety regarding future cancer development rather than objective biological risk [20–22]. Similar age-related patterns have been reported in population-based studies evaluating contralateral prophylactic mastectomy in genetically uninformative or intermediate-risk populations [23].
Although non-luminal tumors and BRCA1 VUS carriers demonstrated numerically higher rates of bilateral mastectomy in our cohort, these differences did not reach statistical significance. This finding mirrors earlier studies indicating that tumor phenotype and specific VUS gene assignment may influence clinical decision-making in practice, despite the lack of robust biological justification [18]. Importantly, current expert consensus and guideline recommendations emphasize that VUS results should not be used to guide surgical or systemic treatment decisions and should instead be managed similarly to negative genetic test results [9, 10, 24].
The contrast between the consistent, biology-driven surgical patterns observed in pathogenic BRCA carriers and the heterogeneous, largely non-biological decision-making seen among VUS carriers represents a key contribution of our study. These findings underscore the ongoing need for improved genetic counseling, standardized interpretation of VUS results, and enhanced clinician education to prevent potential overtreatment in this population. Moreover, the dynamic nature of variant reclassification highlights the importance of periodic re-evaluation of genetic test results as new evidence emerges [25, 26].
Several limitations of this study should be acknowledged. Its retrospective design and the limited number of bilateral mastectomy events among VUS carriers restricted the statistical power of multivariable analyses and necessitated an exploratory approach. Additionally, psychosocial factors, patient preference, and physician recommendation—variables known to influence surgical decisions—could not be fully captured. Nevertheless, the multicenter design and inclusion of both public and private healthcare settings enhance the generalizability of our findings to real-world clinical practice. Moreover, no VUS variants in our cohort were reclassified as pathogenic during the study period, and therefore the clinical impact of variant reclassification on surgical decision-making could not be evaluated.
In conclusion, while pathogenic BRCA1/2 variants are strongly associated with bilateral mastectomy in breast cancer patients, surgical decision-making among BRCA VUS carriers appears largely independent of tumor biology and genetic subtype, with age emerging as the primary influencing factor. These results reinforce current guideline recommendations against using VUS status to guide surgical management and highlight the need for continued efforts to reduce uncertainty and variability in the care of this growing patient population.