16P Monitoring response to neoadjuvant chemotherapy in TNBC using circulating tumor DNA

Triple-negative breast cancer (TNBC), a biologically diverse subtype of cancer, is associated with poor prognosis. Patients (pts) TNBC who achieve pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC) have improved disease free and overall survival. We investigated whether early circulating tumor DNA (ctDNA) measurements could predict to NAC. ctDNA was detected in 94 serial plasma samples (n) from 37 pts (N) (stage I=2, II=19, III=16) tumor-informed assay (SignateraTM, bespoke mPCR-NGS). Pts received standard NAC; collected pre-NAC (n=30), 12 weeks NAC initiation (mid-NAC, n=34), prior surgery (n=15), (n=15). Associations between ultrasound (US) imaging were evaluated. Circulating cells (CTCs) also assessed using CellSearch. pCR defined as the absence invasive axillary lymph nodes surgical specimens. P values measured Student t-test, correlation variables used Pearson analysis. At diagnosis, 90% (27/30) patients, whom 76% (19/25) had clearance by mid-NAC. Imaging at mid-NAC showed that 95% (18/19) cases undetectable evidence partial or (PR/CR), while 1 case progressive disease. After completion NAC, all 19 PR, CR, stable Importantly, 58% (11/19) ctDNA-negative their blood draw achieved pCR, none detectable (N=6) pCR. significantly (P=0.0304). dynamics treatment course correlated rates (P=0.009) volume reduction based on US (P=0.008). CTCs 36% (11/30) pre-NAC, 47% (16/34) mid-NAC, 40% (6/15) post-NAC, 20% (3/15) not Early mid-treatment but during higher rate TNBC. Personalized monitoring feasible may help guide treatment.