98P The added value of whole-body diffusion weighted MRI (WB-DWI/MRI) in staging invasive lobular carcinoma

Invasive Lobular Carcinoma (ILC) challenges standard-of-care imaging, with disease spread being underestimated and missed in many patients. WB-DWI/MRI has demonstrated its added value in detecting lymph node, peritoneal and bone metastases in breast cancer (PMID:35384456). Here, we aimed to assess the added value of WB-DWI/MRI to conventional imaging for staging of patients with ILC. A retrospective single center analysis was performed of all patients with primary ILC undergoing WB-DWI/MRI in addition to standard locoregional and distant imaging staging including: mammography, breast ultrasound, breast MRI, FDG PET/CT, SPECT/CT combined with CT or with chest X-ray/liver ultrasound, at University Hospitals Leuven, Belgium between 2017 and 2023. Diagnostic accuracies between WB-DWI/MRI and conventional imaging staging were compared. Histopathology after surgery or biopsy, or the best valuable comparator including concurrent and follow-up clinical, biological and imaging information were used as reference standard. A total of 93 patients with ILC were included for analysis and their imaging reports were recorded. The diagnostic accuracy of WB-DWI/MRI vs. conventional imaging staging for each region are summarized in the table. WB-DWI/MRI improved detection of tumor sites in the contralateral breast (sensitivity 86.7% vs. 73.3%), detection of ipsilateral axillar lymphadenopathies (sensitivity 92.6% vs. 72.2%) and distant lymphadenopathies (sensitivity 93% vs. 71%). Furthermore, WB-DWI/MRI improved detection of distant metastases (accuracy 96.8% vs. 73.1%). In 25/93 (26.8%) of patients, WB-DWI/MRI detected distant metastases, missed at conventional imaging staging.Table: 98PComparison of WB-DWI/MRI with conventional imagingFocalityContralateral breastIpsilateral axillaDistant lymph nodesDistant metastasesCLSWB-DWI/MRICLSWB-DWI/MRICLSWB-DWI/MRICLS + CDSWB-DWI/MRICDSWB-DWI/MRISensitivity93.8%96.9%73.3%86.7%72.2%92.6%71.4%93.3%63.3%98.3%Specificity95.1%96.7%98.7%98.7%94.9%82.1%100.0%98.7%90.9%93.9%Positive predictive value90.9%93.9%91.7%92.9%95.1%87.7%100.0%93.3%92.7%96.7%Negative predictive value96.7%98.3%95.1%97.5%71.2%88.9%95.2%98.7%57.7%96.9%Accuracy94.6%96.8%94.6%96.8%81.7%88.2%95.7%97.9%73.1%96.8% Open table in a new tab WB-DWI/MRI adds value for primary staging of patients with ILC, by improving the detection of locoregional and distant disease extent. The use of WB-DWI/MRI aids in optimizing treatment choices for patients with ILC.