Importance of circulating tumor DNA analysis at diagnosis in early triple-negative breast cancer patients

Background: Circulating tumor DNA (ctDNA) enables non-invasive evaluation and is considered a promising tool for diagnosis, treatment selection, risk stratification, and disease monitoring. However, while the utility of ctDNA has been demonstrated in advanced-stage cancers, its detection in early breast cancer (EBC) remains limited. This study investigated the characteristics of EBC patients associated with higher ctDNA detectability. Methods: A total of 101 patients with EBC were enrolled. Formalin-fixed paraffin-embedded samples (FFPEs) were obtained from biopsy tissue, and plasma samples were collected before and after neoadjuvant chemotherapy (NAC). Forty-seven breast cancer-related genes were analyzed using next-generation sequencing. The diagnostic performance of ctDNA was evaluated, and logistic regression analyses were conducted to assess the impact of clinical and molecular factors on ctDNA status. Results: The most frequently identified gene was TP53 (FFPE, 66.7%; ctDNA, 46.4%), followed by PIK3CA (FFPE, 36.2%; ctDNA, 17.4%). The diagnostic performance of the three most common genes showed a sensitivity range of 11.1–58.7%, specificity of 78.3–100%, and diagnostic accuracy of 65.2–78.3%. The triple-negative breast cancer (TNBC) subtype exhibited the strongest association with ctDNA detection (odds ratio [OR] 209.50, p = 0.005) in multivariate analysis. Also, those who exhibited ctDNA clearance after NAC had a higher pathological complete response rate compared to those without clearance (38.5% vs. 11.1%, p = 0.238). Conclusions: Our study highlights that ctDNA analysis can complement genetic testing from a single tissue biopsy in breast cancer patients. Furthermore, ctDNA analysis may be particularly important in patients with TNBC.