# Spatial Omics Profiling of Treatment-Naïve Lung Adenocarcinoma with Brain Metastasis as the Initial Presentation

## TL;DR

This study uses spatial proteomics to compare protein expression in brain metastases and lung tumors at initial diagnosis, revealing early immune escape in brain lesions.

## Contribution

First spatial proteomic analysis of treatment-naïve lung adenocarcinoma with brain metastasis as the initial presentation.

## Key findings

- Brain metastases showed reduced immune regulatory proteins like IDO-1, PD-1, and PD-L1 compared to lung tumors.
- Increased pS6 levels in brain metastases suggest activation-induced T-cell death and an immunosuppressive environment.
- Altered protein expression was observed in both tumor and stromal regions of brain lesions.

## Abstract

Brain metastasis is a serious and often early complication in lung adenocarcinoma, the most common type of lung cancer. While many studies have examined treated or advanced cases, little is known about the tumor environment at initial diagnosis. This study analyzed tissue from five patients whose brain metastases were the first signs of lung adenocarcinoma. Using spatial proteomic profiling, we compared protein expression between matched brain and lung tumors. Brain metastases showed reduced immune activity and increased markers of cell growth and immune evasion. These findings highlight the distinct biology of brain lesions even before treatment begins and suggest early immune escape. Understanding these early changes may support future efforts to develop site-specific strategies targeting brain metastases at initial presentation.

Background/Objectives: Brain metastasis (BM) is a common and often early manifestation in lung adenocarcinoma (LUAD), yet its tumor microenvironment remains poorly defined at the time of initial diagnosis. This study aims to characterize early immune microenvironmental alterations in synchronous BM using spatial proteomic profiling. Methods: We performed digital spatial proteomic profiling using the NanoString GeoMx platform on formalin-fixed paraffin-embedded tissues from five treatment-naïve LUAD patients in whom BM was the initial presenting lesion. Paired primary lung and brain metastatic samples were analyzed across tumor and stromal compartments using 68 immune- and tumor-related protein markers. Results: Spatial profiling revealed distinct expression patterns between primary tumors and brain metastases. Immune regulatory proteins—including IDO-1, PD-1, PD-L1, STAT3, PTEN, and CD44—were significantly reduced in brain metastases (p < 0.01), whereas pS6, a marker of activation-induced T-cell death, was significantly upregulated (p < 0.01). These alterations were observed in both tumor and stromal regions, suggesting a more immunosuppressive and apoptotic microenvironment in brain lesions. Conclusions: This study provides one of the first spatially resolved proteomic characterizations of synchronous BM at initial LUAD diagnosis. Our findings highlight early immune escape mechanisms and suggest the need for site-specific immunotherapeutic strategies in patients with brain metastasis.