Phase II study of 3'-deoxy-3'-18F fluorothymidine PET/CT (FLT-PET) in the assessment of early response in locally advanced breast cancer (LABC): Preliminary results of ACRIN 6688.

526 Background: FLT-PET imaging can be exploited as a marker of cellular proliferation and tumor (tm) therapy response. Our primary objective was to determine if early change in tm FLT uptake predicts pathologic complete response (pCR) to neoadjuvant chemotherapy (NAC) in primary tms in LABC pts. The secondary objective was to correlate standardized uptake values (SUVmax) with Ki-67 at baseline and after NAC. Methods: In this phase II study, 51 LABC pts [stage IIA-IIIC] were evaluable for primary objective analysis. NAC was according to standard of care; imaging was not used to change management. All 51 pts underwent FLT-PET imaging at baseline (FLT-1), and after one cycle (FLT-2);43 pts were imaged post-NAC (FLT-3). SUVmax's were averaged for multiple primary tms. The percent change in SUVmax (ΔSUVmax) between FLT-1 and FLT-2 was calculated. Pathologic response, Ki-67 assay and PET/CT were assessed at core labs. The predictive value of ΔSUVmax for pCR was determined by ROC; by area under the curve (AUC)....