Variant allele frequency in circulating tumor DNA correlated with tumor disease burden and predicted outcomes in patients with advanced breast cancer

Purpose In patients with first-line advanced breast cancer (ABC), the correlation between ctDNA variant allele frequency (VAF) and tumor disease burden, and its prognostic value remains poorly investigated. Methods This study included patients with ABC diagnosed at Peking University Cancer Hospital who performed ctDNA test before receiving first-line treatment. Baseline plasma samples were collected for assessing ctDNA alterations and VAF with next-generation sequencing. The sum of tumor target lesion diameters (SLD) was measured with imaging methods according to RECIST 1.1 criteria. Results The final cohort included 184 patients. The median age of the cohort was 49.4 (IQR: 42.3–56.8) years. The median VAF was 15.6% (IQR: 5.4%-33.7%). VAF showed positive correlation with SLD in patients with relatively large tumor lesions ( r = 0.314, p = 0.003), but not in patients with small tumor lesions ( p = 0.226). VAF was associated with multiple metastasis sites ( p = 0.001). Multivariate Cox regression analysis showed that high VAF was associated with shorter overall survival (OS) (HR: 3.519, 95% confidence interval (CI): 2.149–5.761), and first-line progression-free survival (PFS) (HR: 2.352, 95%CI: 1.462–3.782). Combined VAF and SLD improved prediction performance, both median OS and PFS of patients in VAF(H)/SLD(H) group were significantly longer than VAF(L)/SLD(L) group (mOS: 49.3 vs. 174.1 months; mPFS: 9.6 vs. 25.3 months). Conclusion ctDNA VAF associated with tumor disease burden, and was a prognostic factor for patients with ABC. A combination of ctDNA test and radiographic imaging might enhance tumor burden evaluation, and improve prognosis stratification in patients with ABC.