Abstract P4-02-02: Comparison of 18F-FDG PET-CT and 11C-MET PET-CT for assessment of response to neoadjuvant chemotherapy in locally advanced breast carcinoma.

Abstract

Abstract INTRODUCTION: Neo-adjuvant chemotherapy plays an important role in treatment of breast cancer by decreasing the tumor load & it offers an opportunity to evaluate response of primary tumor to chemotherapy. This makes response monitoring crucial in the management of breast carcinoma. Standard anatomical imaging modalities are unable to accurately reflect the response to chemotherapy until several cycles of drug treatment have been completed. Metabolic imaging using tracers like 18F-fluorodeoxyglucose (FDG) as a marker of glucose metabolism or amino acid tracers like L-methyl-11C methionine (MET) have potential role for the measurement of treatment response in breast cancer. AIMS AND OBJECTIVES: To compare FDG PET-CT with MET PET-CT for assessment of response to neoadjuvant chemotherapy, in locally advanced breast carcinoma and to correlate it with clinico-pathological response. METHODS: In our prospective study, 20 patients with histology proven locally advanced breast carcinoma were enrolled. All patients underwent clinical assessment and PET-CT imaging using FDG and MET before and after 3 cycles of neoadjuvant chemotherapy (CAF regimen). Thereafter, all patients were taken for modified radical mastectomy and the resected breast with dissected axillary nodes was sent for histo-pathological analysis. Tumor response to the neoadjuvant chemotherapy was evaluated clinically using WHO criteria and by PET-CT imaging using PERCIST criteria. Responses calculated were compared for statistical significance using paired t- test. RESULTS: Mean SUV in FDG-PET for primary tumor (p < 0.001) and axilla (p = 0.001) were significantly higher than in MET-PET. After three cycles of chemotherapy, clinical size of the primary tumor decreased by 55.76%, mean SUVmax of the primary lesion decreased by 47.21% in FDG-PET (p = 0.16) and by 45.5% in MET-PET (p = 0.167). In axilla, a decrease of 53.39% was seen in mean SUVmax in FDG-PET and 48.37% in MET-PET (p = 0.469) with significant positive correlation (R = 0.53). According to PERCIST criteria, complete response was seen in 5% and 35% patients in FDG-PET and MET-PET respectively, while no patient showed complete response on clinical and histo-pathological assessment. Partial response was seen in 65% patients clinically, 70% in FDG-PET and 55% in MET-PET. In axilla, response was seen in 25% of patients clinically, 75% in FDG-PET and 80% in MET-PET. CONCLUSION: In both FDG-PET and MET-PET, there is a significant decrease in SUVmax of primary breast tumor and axillary metastasis after three cycles of neo-adjuvant chemotherapy correlating with decrease in clinical size. Response evaluation for primary breast tumor by clinical method, FDG-PET and MET-PET was statistically similar and a significant positive correlation was seen. Response evaluation for axillary metastasis by FDG-PET and MET-PET shows higher accuracy than clinical examination. Thus, making PET-CT a valuable monitoring tool for guiding the choice of surgical management of axilla. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-02-02.