Abstract PO1-06-06: Underestimation of metastatic spread in patients with lobular breast cancer: results from the post-mortem tissue donation program UPTIDER

Abstract Background: Invasive lobular carcinoma (ILC) accounts for 15% of all invasive breast cancers (BC) and has a peculiar metastatic spread in comparison to BC of no-special type. Since ILC is less likely to disrupt normal tissue architecture and is usually non-mass forming, imaging of ILC lesions entails many challenges. Insights into pathologic versus radiological metastatic invasion can lead to better diagnostic and monitoring tools for patients with ILC. Here, we compare microscopical findings during autopsy with clinical findings prior to death in patients with metastatic ILC included in our post-mortem tissue donation program UPTIDER (NCT04531696). Methods: UPTIDER was started in November 2020 in University Hospitals Leuven/KU Leuven with inclusion of patients with stage IV BC who were willing to participate. One of the predefined subgroups consisted of patients with primary pure (i.e. not mixed) ILC. Samples were taken from different macroscopically invaded and non-invaded sites. Clinical data on disease progression, imaging, biochemistry and treatment regimens were extracted from patient files. The number of samples that were preregistered as pathological served as a surrogate for lesions that were seen on imaging performed during the treatment of the patient. These samples are compared to microscopical findings of the autopsy. Results: Since the start of UPTIDER, an autopsy has been performed on 6 patients with pure ILC (26.1% of all autopsies). Median age at initial diagnosis was 52 years (range: 37 – 80 years). Three patients (50.0%) had stage IV disease at diagnosis, the others relapsed on average 162.7 months (range: 55 – 358 months) after initial diagnosis. The average time between clinical occurrence of metastases and death was 44.8 months (range: 15 – 83 months). Median number of treatment lines for stage IV disease was 5 (median endocrine lines 2; median chemotherapy regimens 3.5). To follow disease evolution, computed tomography of thorax and abdomen was used for 4 (66.7%) patients and whole-body diffusion-weighted magnetic resonance imaging (WB-DWI/MRI) for the remaining 2 (33.3%). Median time between last premortem imaging and death was 5.9 weeks (range: 1.6 – 16.6 weeks). At autopsy, a median of 26 unique metastases (range: 12-36) were sampled per patient. Table 1 gives an overview on the unique microscopically invaded metastases that were sampled per patient. Only 47.3% of the sampled unique metastases was preregistered. Of all unique metastases, 26.7% appeared macroscopically normal during autopsy. Tissues that appeared normal but turned out to be microscopically infiltrated included liver, stomach, adrenal glands, heart, pericardium, visceral and subcutaneous fat tissue. There were 2 patients with normal appearing, microscopically infiltrated livers. In these patients, elevation of γGT and transanimases was seen in the months prior to death. Conclusions: The disease burden of metastatic ILC reported on premortem imaging does not reflect the microscopical findings at autopsy. One of the priorities of metastatic ILC research should be the development of diagnostic tools to better estimate the extent of the disease. Future analyses of the performed postmortem MRIs in our study can aid in improving the interpretation of WB-DWI/MRI for patients with ILC. For now, clinicians should consider that unexplained clinical and/or biochemical findings might indicate progression of ILC. Table 1: patient overview on performed imaging and unique metastases sampled during autopsy CT = computed tomography; ER = estrogen receptor; HER2 = human epidermal growth factor receptor 2; pt = patient; WB-DWI MRI = whole-body diffusion-weighted magnetic resonance imaging *exclusion of samples of patient 2012 since no preregistration was performed for this patient due to unexpected death Citation Format: Karen Van Baelen, Gitte Zels, Maxim De Schepper, Marion Maetens, Josephine Van Cauwenberge, Tatjana Geukens, Kristien Borremans, François Richard, Amena Mahdami, Ha-Linh Nguyen, Sophia Leduc, Anirudh Pabba, Ann Smeets, Ines Nevelsteen, Patrick Neven, Hans Wildiers, Vincent Vandecaveye, Wouter Van Den Bogaert, Giuseppe Floris, Christine Desmedt. Underestimation of metastatic spread in patients with lobular breast cancer: results from the post-mortem tissue donation program UPTIDER [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-06-06.