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

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=0.025).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=0.011).Patients with mTBI decrease to less than 0.02%at the first tumor evaluation had longer progression-free survival and overall survival(P<0.001 and P=0.007,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<0.001 and P=0.036,respectively),as well as in the cohort in which computed tomography scans were defined as representing stable disease(P=0.027 and P=0.015,respectively).The mTBI in ctDNA detected in liquid biopsies is a potential biomarker of therapeutic response and prognosis in patients with metastatic breast cancer.