Gastric cancer (GC) is a prevalent and deadly disease, ranking as the fifth most common cancer and the third leading cause of cancer-related mortality worldwide (Siegel et al., 2021). The majority of GC patients are diagnosed at an advanced stage, resulting in a median survival of only 12 to 15 months (Siegel et al., 2021, Smyth et al., 2020). Neoadjuvant chemotherapy plus anti-PD1 therapy has showed great potential for advanced gastric tumors before attempting a curative resection (Lin et al., 2021, Jiang et al., 2022, Tang et al., 2022, Guo et al., 2022, Yin et al., 2022, André et al., 2023). Encouraging preliminary results have been observed for the combination of chemotherapy and anti-PD1 therapy, regardless of PD-L1 expression status (Bang et al., 2019, J Tabernero and Bang, 2019). However, clinical responses to chemotherapy and anti-PD1 therapy varied among different patients (Xavier et al., 2022). Most patients have primary resistance and do not benefit from anti-PD1 therapy (Baxter et al., 2021). Some patients experienced early progression, with progressive disease rates exceeding 10% (Italiano et al., 2022, Li et al., 2021). Those who do respond often develop acquired resistance (Baxter et al., 2021). Resistance of tumor components to chemo and immuno-therapy impedes the enhancement of outcomes in gastric cancer.

Immunosuppressive tumor microenvironment (TME), characterized by immune cell infiltration and immunomodulatory molecules, is a major obstacle to chemo and immune-therapy resisitance (Vitale et al., 2019, Xing et al., 2023). Tumor-associated macrophage (TAM) is widely acknowledged as a primary contributor to drug resistance in gastric cancer. Single-cell RNA sequencing (scRNA-seq) has emerged as a powerful tool for identifying TME signature associated with anti-PD1 therapy response and resistance in various cancers (Au et al., 2021, Lei et al., 2021, Wang et al., 2021a, Zhang and Zhang, 2020, Du et al., 2023). However, the specific scRNA-seq signature to chemo and immuno-therapy response and resistance in GC remains unclear.

To address this gap in knowledge, we propose a multi-omics analysis approach to investigate the differences at the cellular and spatial levels between response and resistance to anti-PD1 combined with chemotherapy in advanced GC patients. Specifically, we will analyze the surgical tissue samples from five treatment-responsive patients and five resistant patients. By integrating scRNA-seq and multiplex immunohistochemistry (mIHC) techniques, we aim to identify novel cellular and molecular features associated with treatment resistance, for personalizing therapeutic strategies and enhancing treatment outcomes in GC.

It is important to acknowledge the limitations of scRNA-seq, such as the lack of cell spatial information, focus on transcriptional rather than protein expression, and challenges in implementing it in larger cohorts (Lei et al., 2021, Wen et al., 2022). However, these limitations can be partially overcome through the complementary use of mIHC, which enables the detection of multiple markers from a single tissue sample and provides comprehensive information about cell composition and spatial arrangement (Ding et al., 2022, Jia et al., 2022). Nevertheless, mIHC also has its limitations, including the restricted number of markers that can be simultaneously detected (Tan et al., 2020).

In summary, our study aims to elucidate the cellular and spatial characteristics associated with resistance to anti-PD1 therapy combined with chemotherapy in advanced GC patients. By employing a multi-omics approach, we hope to uncover novel cellular and molecular features that could serve as potential therapeutic targets, ultimately improving the prognosis and overcoming drug resistance for GC patients.