Three or More Breast Cancer Foci Increase Specific Mortality Risk

Prognostic Uncertainty in Multifocal Breast Malignancy

Breast cancer remains a leading cause of oncology-related mortality globally, necessitating precise risk stratification to optimize surgical and systemic interventions [1]. While traditional staging focuses on the size of the primary lesion and nodal involvement, the clinical significance of multifocality, defined as the presence of multiple synchronous tumor foci within the same breast, remains a subject of debate [2]. Current management strategies have evolved from mandatory mastectomy to include breast-conserving therapy for multifocal disease, provided that negative margins can be achieved [3, 4]. However, meta-analyses have produced conflicting data regarding whether these patients face a higher risk of systemic recurrence or breast cancer-specific death compared to those with unifocal tumors [5, 6]. A new national cohort study now provides evidence on how the number of invasive foci influences long-term survival outcomes.

Analysis of a National Swedish Cohort

The researchers conducted a comprehensive population-based analysis using data from the Breast Cancer Data Base Sweden 3.0, a national registry that integrates clinical information to track oncological outcomes. This study cohort included 71,607 women who underwent surgery for invasive breast cancer across Sweden between 2008 and 2019. By utilizing a nationwide database, the authors ensured a representative sample of patients treated within a modern clinical framework, providing sufficient statistical power to evaluate the impact of tumor distribution on long-term survival. This large sample size is particularly important for detecting subtle differences in survival rates that might be missed in smaller, single-institution studies.

Correlation with Advanced Tumor Characteristics

Within this large-scale cohort, the researchers categorized patients based on the number of distinct tumor centers identified during pathological examination. The majority of the population, consisting of 59,445 women (83.2%), presented with unifocal breast cancer, which is characterized by a single invasive lesion. In contrast, multifocal disease was identified in a significant minority of the participants. Specifically, 7,286 women (10.2%) were diagnosed with multifocal breast cancer containing two invasive foci, while 4,688 women (6.6%) presented with three or more invasive foci. This granular classification allowed the investigators to evaluate whether an increasing number of tumor centers independently correlates with breast cancer-specific mortality beyond traditional staging metrics.

Long-Term Survival and Mortality Risk

The analysis of the Swedish cohort demonstrated that the spatial distribution of malignancy is closely linked to established metrics of tumor progression. The researchers found that multifocal breast cancer was associated with higher T-categories compared to unifocal breast cancer. In the context of the TNM staging system, the T-category, a classification denoting the size and local reach of the primary tumor, tended to be more advanced in patients with two or more invasive foci. This association suggests that multifocality may serve as a clinical marker for a more proliferative or locally invasive disease phenotype at the time of surgical intervention. Furthermore, the data showed that multifocal breast cancer was associated with higher N-categories compared to unifocal breast cancer. The N-category, the classification of regional lymph node involvement based on the number and site of positive nodes, was consistently higher in the multifocal groups, indicating a greater likelihood of nodal metastasis at the time of diagnosis. While these correlations suggest that multifocal tumors are often detected at a more advanced stage, the researchers sought to isolate the specific impact of the number of foci on patient outcomes to determine if multifocality carries independent prognostic weight.

Implications for Clinical Risk Stratification

The researchers monitored the cohort over a median follow-up time of 5.96 years, with an interquartile range, the middle 50 percent of the data, spanning 3.07 to 8.80 years. During this longitudinal period, distinct survival trajectories emerged based on the number of invasive foci present at the time of surgical intervention. The breast cancer-specific 10-year survival probability for women with unifocal breast cancer was 88.5%. In contrast, survival rates were lower for patients with multifocal disease. Specifically, the breast cancer-specific 10-year survival probability for women with 2 foci was 86.5%, while the probability for those with 3 or more foci was 86.1%. To determine if multifocality serves as an independent prognostic marker, the authors conducted a multivariable analysis, a statistical method that isolates the effect of one variable while controlling for others, adjusted for patient and tumor characteristics. This analysis revealed that the hazard ratio for breast cancer-specific death was 1.17 for cases with 3 or more foci compared to unifocal cases. The 95% confidence interval for this hazard ratio, the range of values within which the true effect is likely to fall, was 1.03 to 1.32, confirming that the increased risk of mortality is statistically significant. Clinicians should note, however, that there was no statistically significant difference in overall survival between the three groups. This distinction is critical for prognosis, as it indicates that while the presence of three or more foci specifically increases the risk of dying from breast cancer, it did not significantly alter the risk of death from all causes within the observed timeframe. The researchers concluded that multifocality carries additional prognostic information over traditional tumor characteristics, suggesting that the biological burden of the disease may be underestimated in multifocal cases when using standard staging protocols alone. For the practicing clinician, these data suggest that patients with three or more foci may benefit from more intensive surveillance or a lower threshold for adjuvant systemic therapy.

References

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