Patient-derived explant model of appendiceal cancer.

Abstract

4160 Background: Appendiceal cancers (AC) are rare with 5-year survival of 15% for high grade (HG) adenocarcinomas and 75% for low grade (LG) mucinous neoplasms. There is limited literature on the AC tumour microenvironment (TME) in disease progression and drug resistance. Ex vivo cultures, such as patient derived explants (PDEs), have been used for other solid tumours to test anticancer agents, explore the TME, and are being developed as personalised models. The aim of our study was to develop a PDE model of AC, preserve the TME, study the biological profile of AC and test novel therapies. Methods: Fresh tissue was collected during cytoreductive surgery (CRS) from consenting patients with AC with peritoneal disease, Jul 2020-Mar 2021. Tissues from 10 patients were dissected and cultured as PDEs under varying conditions of tissue size, media, matrix support and duration (Table). Uncultured Day 0 tissues and PDEs were fixed in formalin prior to paraffin embedding (FFPE). Immunohistochemical staining was performed on sections of FFPE tissue to assess viability with antibodies against the tumour marker, Cytokeratin-20 (CK20), and cell death marker, cleaved caspase 3 (CC3). Tissue architecture was rated on a 4-point scale (MS, J-SS). Cancer cells were counted in 6 Day 0 samples and PDEs from 3 patients using QuPath v0.3.2. Apoptotic index (AI) was calculated as the proportion of cells positive for CC3 divided by the number of total CK20 positive cells. Results: The mean proportion of tumour and mucin in the tissues was 3% (0-60%) and 39% (0-95%) respectively. Day 0 samples were viable with mean AI of cancer cells 7% (0-4%). Tissue architecture was maintained, as compared to Day 0 control, for varying sizes of PDE and culture durations up to 4d. More small or medium-sized PDEs had improved architecture compared to large sized PDEs (Table). PDEs at 4d had poorer architecture compared to at 1-3d. There was improved architecture in PDEs using enriched media with support factors compared to base media, and in specimens with matrix support compared to none. The mean AI of PDE cancer cells was 21% (0-92%) and 51% of PDEs had no cancer cell death. Conclusions: This is the first study demonstrating that AC tissue is amenable to ex vivo culture as PDEs. The optimal PDE model was <10mm tissue placed on a gelatine sponge in enriched media for 1-3d. PDEs had preserved tissue architecture and viability compared to uncultured tissue. Protein expression was in keeping with the original tumour. We plan to use this model to test anticancer agents and explore the TME of AC.[Table: see text]