Abstract BACKGROUND: Histologic and molecular differences between primary breast cancer and their subsequent metastases are well-established. Characterization of this heterogeneity may provide important information for both diagnosis and prognosis. Tissue donation via autopsy can aid in characterizing the microenvironment and understanding organ tropism. We describe the implementation, results, and challenges of a cohesive program of post-mortem tissue procurement in patients with breast cancer. METHODS: Prior to formalization of the program, three autopsies were performed without specific operating procedures. In 2016, formal input from patients, their families, clinicians, and pathology technicians helped to operationalize a formal tissue donation program. Ten autopsies have been performed to date. Demographic and clinical data were collected for these patients through retrospective chart reviews. When available, primary tumor tissue and any prior metastasis which were biopsied or surgically resected were acquired from clinical archives at our institution, or requested from outside facilities for future analyses. RESULTS: Between October 2011 and April 2019, autopsies were performed on 1 male and 9 female patients. Time from primary to metastatic disease was an average of 4 years. The median age at the time of death was 56 years (range 37-73). The average time from diagnosis of metastatic disease to consent to autopsy was 30 months. Although the majority of patients died outside the hospital (70%), the mean time between death and the start of autopsy was 4.7 hours. Samples of metastatic tissue were collected in all patients postmortem. There was an average of 16 samples collected from various sites that included both normal and metastatic tissue. The most common sites were the liver (80%), lung (70%), and lymph nodes (70%). Immunohistochemical analysis of metastatic tumors revealed intrapatient heterogeneity in ER, HER2 and Ki67 staining. TABLE 1: CLINICAL COURSE OF PATIENTSN=10 patientsPatients (%)Age at Diagnosis, years (median)46.7 (24.9-57.8)GenderFemale9 (90)Male1 (10)AJCC stage at initial presentationStage 13 (30)Stage 23 (30)Stage 33 (30)Stage 41 (10)Molecular SubtypesHR+/HER 2-6 (60)HR+/HER 2+2 (20)HR-/HER 2-2 (20)HR-/HER 2+0 (0)Time from initial diagnosis to metastatic disease, years (median)4.3 (0-12.8)Tissue of Metastases Obtained While AliveYes4 (40)No6 (60)Median age at time of death, years56.5 (37-73)Total Survival (dx to death), years (median)7.7Metastatic Survival (mets to death), years (median)3.3 TABLE 2: POST MORTEM TISSUE DONATION PROGRAMTime from Metastatic Diagnosis to Consent for Autopsy, months (median)30.3Time from Consent for Autopsy to Death, months (median)10.25Location of DeathHome5 (50)Hospital3 (30)Inpatient Hospice Facility2 (20)Time from death to starting autopsy, hours (median)4.68Time to complete autopsy, hours (median) N=72.82Number of Samples Collected During Autopsy (median)16.2 (3-27)Sites for Metastatic Tissue Procurement Postmortem8 (80)Liver7 (70)Lung7 (70)Lymph Nodes4 (40)Brain4 (40)Ascitic Fluid3 (30)Bone2 (20)Adrenal2 (20)Pericardium2 (20)Pleural Effusion1 (10)Chest Wall1 (10)Gall Bladder1 (10) CONCLUSION: Post-mortem tissue donation programs allow procurement of tissue that would otherwise be inaccessible in the living patient. Histological examination and immunohistochemical assessment of key biomarkers will be used to further characterize the tissue collected ante-mortem and post-mortem. This data combined with the clinical history and longitudinal specimens will help us better understand how intra- and inter-tumor heterogeneity play a role in the clinical course of breast cancer. Also, as we establish the program, we will identify barriers that need to be addressed in order to optimize the process. Citation Format: Tara Hyder, Lori Miller, Jennifer M Atkinson, Zoe Wecht, Ashuvinee Elangovan, Kai Ding, Nolan Priedigkeit, Zheqi Li, Tiantong Liu, Laura Savariau, Fangyuan Chen, Oscar Lopez, Dayne Ashman, Daniel Geisler, Jacob A Smith, Rachel Jankowitz, Priscilla F McAuliffe, Shannon Puhalla, Humberto E Trejo Bittar, Jeffrey S Nine, Peter C Lucas, Adam Brufsky, Steffi Oesterreich, Adrian V Lee, Margaret Rosenzweig. Implementation of a breast cancer post-mortem tissue donation program [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-21-02.