The molecular tumor burden index as a response evaluation criterion in breast cancer

Abstract

Circulating tumor DNA (ctDNA) is a potential biomarker of prognosis and therapeutic response. We conducted this study to explore the role of the molecular tumor burden index (mTBI) in ctDNA as a therapeutic response and prognostic biomarker in a larger cohort prospective phase III randomized multicenter study. We collected 291 plasma samples from 125 metastatic breast cancer patients from the CAMELLIA study (NCT01917279). Target-capture deep sequencing of 1021 genes was performed to detect somatic variants in ctDNA from the plasma samples. The pretreatment mTBI value was correlated with tumor burden ( P \u2009=\u20090.025). Patients with high-level pretreatment mTBI had shorter overall survival than patients with low-level pretreatment mTBI, and the median overall survival was 40.9 months and 68.4 months, respectively ( P \u2009=\u20090.011). Patients with mTBI decrease to less than 0.02% at the first tumor evaluation had longer progression-free survival and overall survival ( P \u2009<\u20090.001 and P \u2009=\u20090.007, respectively). The mTBI has good sensitivity to identify complete response/partial response and progressive disease based on computed tomography scans (88.5% and 87.5%, respectively). The patients classified as molecular responders had longer progression-free survival and overall survival than the nonmolecular responders in the overall cohort ( P \u2009<\u20090.001 and P \u2009=\u20090.036, respectively), as well as in the cohort in which computed tomography scans were defined as representing stable disease ( P \u2009=\u20090.027 and P \u2009=\u20090.015, respectively). The mTBI in ctDNA detected in liquid biopsies is a potential biomarker of therapeutic response and prognosis in patients with metastatic breast cancer.