Early change in 18-fluorodeoxyglucose (FDG) uptake on positron emission tomography (PET) to predict response to preoperative systemic therapy (PST) in HER2-negative primary operable breast cancer: Translational breast cancer research consortium (TBCRC008).

Abstract

10509 Background: PST allows for improved surgical outcomes and response assessment without compromising long term outcomes. PST is an attractive model for assessing surrogate markers of response to therapy. We hypothesized that changes in tumor standardized uptake values corrected for lean body mass (SUL) max on FDG- PET by cycle 1 day 15 (C1D15) of therapy would predict pathological complete response (pCR) to PST in women with stage 2-3, grade 2-3, HER2-negative breast cancer. Methods: TBCRC008 is a multicenter placebo-controlled trial that investigates pCR following 12 weeks of preoperative carboplatin and albumin-bound paclitaxel with or without vorinostat. FDG-PET followed by tumor biopsies were performed at baseline and C1D15. We correlated % reduction in SULmax on FDG-PET (PERCIST 1.0; Wahl RL, J Nuc Med 2009) with pCR (no invasive cancer in breast/axilla). We compared % reduction in SULmax between responders (pCR) and non responders (no pCR) using nonparametric Wilcoxon rank sum test. We explored association of % reduction in SULmax at pre-specified cutoff with response using Fisher’s exact test and logistic regression. We correlated baseline, C1D15, and % change in Ki67 at C1D15 with pCR. Results: Accrual is complete. Of 62 women enrolled (10/2009-11/2011), 40 have completed study PST and surgery (median age 47.5 [range 30-68], ER-positive 67%). Overall pCR was 26%. In an intent to treat analysis (n=39), we observed a significant difference in median % reduction in SULmax between responders vs not (66.6% vs 32.4%, p <0.001). We observed a higher proportion of reduction in SULmax ≥ 60% in responders vs not (80% vs 3.5%, p <0.001). The differences in baseline, C1D15 and % change in Ki67 were not significant between responders and non-responders. Conclusions: Change in SULmax on FDG-PET 15 days after initiating PST was significantly greater in patients with pCR versus no pCR. Future studies will determine whether altering therapy based on early changes in SULmax will improve pCR. Unblinded data from all participants will be presented at the meeting.