Multidimensional spatial characterization of the tumor microenvironment (TME) in synchronous melanoma metastases (SMM) to yield insights into mixed responses to therapy in metastatic melanoma (MM) patients (pts).

Abstract

9575 Background: Although both targeted and immune therapies have significantly improved outcomes for mm pts, only a minority of pts experience durable responses with many pts with multiple SMM demonstrating differential responses to therapy. We performed multidimensional spatial characterization of immune markers in SMM from mm patients treated with targeted and immune therapies to improve our understanding of correlations and determinants of response. Methods: NanoString's Digital Spatial Profiling research platform was used on 6 SMM from 3 pts (treatment-naïve; BRAF + MEK targeted therapy treated; anti-PD-1 immunotherapy treated) for 30 immune and signaling proteins. For analysis, we selected and compared immune-rich (CD45+) and tumor-rich (S100B+) regions across SMM. Results were compared to lesion-specific clinical responses. Results: Striking differences in patterns of expression across SMM from individual pts were detected, including in Ki67, CD68 myeloid cells, and the potent immunosuppressor B7-H3. SMM progressing after targeted therapy demonstrated higher pAKT and PD-L1 expression, consistent with described resistance mechanisms. Large differences in expression of PD-L1 were noted following anti-PD-1 therapy, which could contribute to heterogeneous responses. Differential expression patterns in the TME associated with response were also detected, including in increases in CD4 and CD14 cells in progressing lesions. Conclusions: Striking differences in responding and non-responding SMM were observed, providing potential explanations for the heterogeneous clinical responses frequently observed in mm pts. Studies are ongoing to further characterize interactions and spatial distribution of cell types, as well as integrate these findings with previous molecular and immune profiling data (whole exome sequencing, gene expression profiling, flow cytometry, IHC, TCR sequencing) in these and additional SMM to identify actionable strategies to homogenize responses across metastases in mm pts.