Abstract PS3-27: 18F-FDG-PET/CT and MRI in the assessment of neoadjuvant chemotherapy treatment response in breast cancer. Correlation with pathological response

Abstract Introduction: Residual cancer burden (RCB) after neoadjuvant chemotherapy (NAC) can accurately predict disease recurrence and survival in breast cancer. In this context, end of treatment (EOT) image-guided response assessment could be useful to adapt treatment for individual patients. Our main objective was to assess the effectiveness of 18F-FDG PET/CT and MRI in determining NAC response. Methods: Patients with surgically resectable breast cancer (stages II-III) were prospectively included and evaluated with 18F-FDG-PET/CT and MRI before and after standard-of-care neoadjuvant chemotherapy (NAC). Ultrasound guided breast biopsy was performed before NAC and pathologic examination with residual cancer burden (RCB) scoring was performed after surgery. Standard uptake values (SUVmax and SUVmean) from baseline PET scans were measured. EOT images results were compared with RCB scores to assess the sensitivity and specificity of (EOT) 18F-FDG-PET/CT and MRI images. A multinomial logistic regression was performed to assess predictors of pathological response. A p-value of 0.05 was considered significant. Results: 30 patients were included, with 25% showing complete pathological response. EOT 18F-FDG-PET/CT images had a sensitivity of 55% and specificity of 100% to predict RCB > 0, while EOT MRI had a sensitivity of 65% and specificity of 66,6%. Luminal tumors showed significant lower baseline SUVmean and SUVmax values than triple-negative tumors. Ki67 expression didn´t correlate with treatment outcome. High estrogen receptor expression level was significantly associated with non-complete pathological response and higher false negative rates in both EOT 18F-FDG-PET and MRI images (7/8 in PET and 6/7 in MRI). Conclusions: 18F-FDG-PET / CT could be a useful diagnostic tool to assess neoadjuvant chemotherapy treatment response in breast cancer, showing greater specificity than MRI to predict pathological response. A high expression of estrogen receptors could lead to a high rate of false negative findings, both in PET and MRI. A greater number of cases is required to validate these findings. Citation Format: Marco Guarin, M. Eugenia Azar, Carolina Tinetti, M. Dolores Mansilla F., Mauro Namias, Pilar Carballo, Lucia Santamarina, Jorgelina Cavallero, Romina Moreau, Christian Gonzalez, Valeria Caceres, Eduardo Gonzalez, Gabriel Bruno. 18F-FDG-PET/CT and MRI in the assessment of neoadjuvant chemotherapy treatment response in breast cancer. Correlation with pathological response [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS3-27.