# A Study on the Diagnostic and Prognostic Value of Extrachromosomal Circular DNA in Breast Cancer

## TL;DR

This study explores how extrachromosomal circular DNA (eccDNA) can help diagnose and predict outcomes in breast cancer patients.

## Contribution

The study introduces a novel diagnostic and prognostic model based on eccDNA features in breast cancer.

## Key findings

- EccDNA in breast cancer tissues contains more functional elements and repetitive sequences linked to tumor and immune pathways.
- The diagnostic model using eccDNA achieved an AUC of 0.83, with repetitive elements and enhancer features being most informative.
- The prognostic model reached an AUC of 0.78, showing that repetitive elements are strongly associated with patient outcomes.

## Abstract

Objectives: To investigate the clinical diagnostic and prognostic value of extrachromosomal circular DNA (eccDNA) in breast cancer, eccDNA profiles were constructed for 81 breast cancer tumor tissues and 33 adjacent non-tumor tissues. Methods: The distribution characteristics of eccDNA across functional genomic elements and repetitive sequences were systematically analyzed. Furthermore, a diagnostic model for differentiating malignant and normal breast tissues, as well as a prognostic prediction model, was developed using a random forest algorithm. Results: EccDNA in breast cancer tissues harbor a higher proportion of functional elements and repetitive sequences, with their annotated genes significantly enriched in tumor- and immune-related pathways. However, no significant differences in eccDNA features were observed across breast cancer subtypes or pathological stages. In the validation cohort, the eccDNA-based diagnostic model achieved an AUC of 0.83, with repetitive elements and enhancer-associated features contributing the most to diagnostic performance. The prognostic model achieved an AUC of 0.78, with repetitive element annotations also showing strong prognostic relevance. Conclusions: These findings highlight the promising potential of eccDNA in the development of precision diagnostics and prognostic systems for breast cancer.