Abstract P6-15-02: Automated tissue dissection of dermal lymphatic emboli in inflammatory breast cancer enhances accuracy of transcriptional analysis

Introduction: Inflammatory breast cancer (IBC) is a clinical diagnosis that spans all breast cancer subtypes. The clinical course of IBC is associated with poorer outcomes than molecular subtype-matched non-IBC and represents an unmet need in breast cancer therapy. IBC is characterized by invasive dermal lymphatic tumor emboli (DLTE) resulting in erythema and edema of the breast. This suggests a common molecular theme, which if identified and targeted, could reduce mortality. Although several genomic and transcriptomic studies of IBC have been performed, no definitive genomic drivers have been identified. We hypothesized that the genomic features of IBC remain undiscovered because only the primary tumor has been analyzed, rather than the population of tumor cells responsible for the phenotype (i.e. DLTE). However, analysis of DLTE is challenging due to lack of effective technologies to purify these cells from the more abundant stroma. Methods: We utilized the Millisect automated dissection (AD) technology, which can selectively recover tissue from targeted areas as small as 200µ2 on standard FFPE sections, on matched skin with DLTE and primary tumor slides from 7 post-treatment IBC mastectomy specimens. We performed RNA sequencing (RNAseq) on AD-enriched primary tumor and DLTE, on full sections from the same samples (including stroma and tumor) and on tissue remaining post-AD (containing residual stroma after tumor cell extraction). Results: RNAseq analysis in AD-enriched primary tumor and DLTEs identified unique transcriptional patterns upregulated in DLTE indicative of lymphatic trafficking (e.g. CCL21), immunosuppression (e.g. S100A9/calprotectin), and myofibroblastomic differentiation (e.g. CD34, desmin, alpha-smooth muscle actin). Gene set enrichment corroborated these inferences, demonstrating DLTE enrichment of gene sets involved in chemokine/trafficking, tumor stemness, and smooth muscle contraction/migration. These gene sets were not apparent in samples extracted from the full sections. Conclusions: Automated dissection technology enables specific investigation on the limited epithelial material that comprises inflammatory breast cancer involving dermal lymphatics. Further investigation, with cohort expansion to increase sample size and statistical power, will focus on pre-treatment skin biopsies with DTLE and matched breast tumor tissue. We expect this will yield novel insights into the biology and treatment of this unique phenotype. Citation Format: Jennifer M Giltnane, Justin M Balko, Nickles Dorothee, Sarajane Nghiem, Anneleen Daemen, Emmanuel Naouri, Amy A Lo, Beth T Harrison, Emily J Schlosnagle, Charles Havnar, Carmina Espiritu, Daniel G Stover, Beth A Overmoyer. Automated tissue dissection of dermal lymphatic emboli in inflammatory breast cancer enhances accuracy of transcriptional analysis [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 P6-15-02.