Proteomic characteristics of lung adenocarcinoma tumors that are small but highly invasive

Understanding the molecular mechanism of early lymph node metastasis among lung adenocarcinoma (LUAD) is essential for developing novel therapeutic agents. Proteomic studies helped generate molecular landscape for LUAD. However, the molecular basis of early lymph node metastases remains unknown in patients with LUAD.

Surgically resected LUAD tissues and paired normal tissues were selected from 25 patients with stage pT1bN2M0 (group of metastases [GM]) and 27 patients with stage T2b‐3N0M0 (group of large primary focus, GL) who had not undergone any anti‐tumor treatment. 4D‐Label‐free proteomics sequencing was performed among these tissues. The clinicopathological information was retrieved from the electronic medical record system in Guangdong Provincial People's Hospital.

Compared with GL tumor tissue, 89 upregulated and 155 downregulated proteins were identified in GM tumor tissue. Upregulated proteins of GM were enriched in the ECM‐receptor interaction and PI3K‐AKT pathway under Kyoto Encyclopedia of Genes and Genomes enrichment analysis. And then, the median disease‐free survival (DFS) of GM phenotype patients was used as the cut‐off value, and GM was divided into two groups with significantly different survival outcomes (DFS good vs. DFS Poor: DFS: p < 0.0001; overall survival: p = 0.0017). All members of the Microchromosome maintenance protein family were highly expressed in the DFS‐poor group, especially MCM2. Proteome‐based stratification of LUAD revealed three subtypes (S‐2, S‐2, and S‐3) related to different clinical and molecular features. S‐3 had higher catabolism‐related pathways enriched, such as amino sugar and nucleotide sugar metabolism and fructose and mannose metabolism, which has the worst prognosis (S1 vs. S2 vs. S3, RFS: p = 0.042).

Proteomics analyses revealed that the activation of the extracellular matrix and intracellular signal transduction might be the driving mechanisms for early lymph node metastasis. Higher expressed cell proliferation related pathways of early lymph node metastatic LUAD may accelerate the recurrence after curative surgery. Three proteomic subgroups of LUAD with distinct molecular and clinical characteristics were identified, the one of which characterized by enrichment of catabolism‐related pathways displayed the worst survival data.