Gastric cancer (GC) is the sixth most common worldwide malignancy and the third leading cancer cause of death. Early diagnosis and effective after-surgical monitoring can significantly improve survival rates. Previous studies have revealed several serum biomarkers that are elevated in GC patients, including CEA, CA19-9, and CA72-4. However, sensitivity of these biomarkers is below 30%. Identification of more sensitive and specific to GC markers is critical for individualized therapy of this disease. Here we developed an approach for single-cell transcriptomic data analysis that identifies secretory proteins that are abundantly expressed in GC cells and that could be measurable in the blood. Using early GC scRNA-seq data, we identified 19 secretory proteins significantly overexpressed in GC cells. Notably, 4 proteins (IL32, KLK10, KLK7, OLFM4) have demonstrated more superior sensitivity in comparison to conventional serum markers in previous studies. Moreover, 2 proteins, F12 and CFD, were not previously associated with GC and were not utilized for serum-based testing of other malignancies. Proposed approach has a high potential to be used for serum marker identification in other types of cancers and presented here data could be a source for the development of more sensitive and specific diagnostic panel for early gastric cancer detection and patient post-treatment monitoring.