| Molecular classification | Grade I recommendations | Grade II recommendations | Grade III recommendations |
|---|---|---|---|
| Following a pathological diagnosis of gastric cancer, molecular profiling a should be undertaken, directing treatment based on the molecular classification. | HER2 assessment is recommended for all cases of gastric adenocarcinoma b ‐ d (Evidence 1A); |
The assessment of PD‐L1 expression status is advised for patients scheduled to undergo treatment with PD‐1/PD‐L1 inhibitors h (Evidence 2A) |
Detection of the NTRK fusion gene i Detection of the Claudin18.2 expression j (Evidence 2B) |
|
Evaluation of MSI/dMMR status in all new gastric cancer cases is recommended e ‐ g (Evidence 1B) |
Abbreviations: HER2, human epidermal growth factor receptor 2; MSI, microsatellite instability; dMMR, deficient DNA mismatch repair; PD‐L1, programmed death‐ligand 1; NTRK, neurotrophic tyrosine receptor kinase.
Notes:
In cases of treatment failure following standard therapy for advanced gastric cancer, NGS can aid in identifying potential therapeutic targets. It is crucial to prioritize certified platforms and products that adhere to stringent quality control and standardized operational processes are recommended to ensure the reliability of the obtained results.
HER2 status has shown correlation with the response and prediction of survival in patients with advanced gastric cancer receiving trastuzumab treatment. Therefore, it is advisable to conduct HER2 status testing for all gastric cancer [24, 25, 26, 27].
According to studies [28, 29], high‐throughput sequencing‐based serial circulating tumor DNA (ctDNA) genotyping emerges as an efficient approach for tracking resistance to trastuzumab, relying on variations in HER2 copy numbers in HER2‐positive gastric cancer. In cases where tissue biopsy is unattainable, evaluating HER2 amplification through liquid biopsy stands as a promising alternative. Additionally, HER2 amplification detected from ctDNA may serve as a means to monitor the response for gastric cancer patients to trastuzumab.
IHC and in situ hybridization (ISH) techniques utilized for HER2 assessment must strictly adhere to the “Guidelines for HER2 detection in gastric cancer (2016)” [30]. All associated tests (IHC, FISH/double signal in situ hybridization [DSISH]) should utilize kits approved by the China Food and Drug Administration (CFDA).
In recent years, immune checkpoint inhibitors targeting programmed death protein‐1 (PD‐1) and its ligand‐1 (PD‐L1) have gained significant attention in the field of tumor immunotherapy. For patients planned for immunotherapy, it is advisable to assess MSI/MMR status and explore the link between PD‐L1 expression and tumor mutational burden (TMB). The correlation of Epstein‐Barr virus (EBV) status with immunotherapy is still undergoing comprehensive elucidation.
MMR protein detection involves the immunohistochemical assessment of MutL homolog 1 (MLH1), postmeiotic segregation increased homolog 2 (PMS2), MSH2, and MSH6 proteins within the nucleus. The absence of any of these four proteins categorizes the patient as dMMR, whereas the presence of all four proteins classifies the patient as proficient MMR (pMMR).
MSI detection is recommended using the 5 microsatellite loci (BAT25, BAT26, D5S346, D2S123, D17S250) proposed by the US National Cancer Institute (NCI). Grading criteria are defined as follows: microsatellite stability (MSS) indicates stability across all 5 loci, MSI‐L is identified when 1 locus displays instability, and MSI‐H is diagnosed when ≥2 loci exhibit instability. MSI typically arises due to mutations or function defects in MMR genes, reflected in MMR protein analysis. Consequently, dMMR can be equated to MSI‐H, while pMMR corresponds to MSI‐L or MSS.
It is advisable to utilize certified antibodies and platforms for PD‐L1 testing to ensure the reliability of test results. For a sample to be deemed suitable for PD‐L1 assessment, a minimum of 100 tumor cells should be present within the sample. The testing report is recommended to use either the Combined Positive Score (CPS) or Tumor Area Positivity (TAP) scoring. CPS is calculated as follows: CPS = (the total number of PD‐L1‐stained cells [including tumor cells, macrophages, and lymphocytes] / total number of tumor cells under the microscope) × 100 [31]. TAP is calculated as follows: TAP = (percentage of PD‐L1‐positive tumor cells and tumor‐associated immune cells [including macrophages and lymphocytes] / total tumor area) × 100 [32, 33].
The U.S. FDA has approved the use of tropomyosin receptor kinase (TRK) inhibitors (i.e., larotrectinib or entrectinib) for patients with solid tumors displaying neurotrophic tyrosine receptor kinase (NTRK) gene fusion. In gastric cancer patients unresponsive to standard treatment, the detection of NTRK gene fusion can be accomplished through various methods. While immunohistochemistry serves as a fast and convenient preliminary screening method, its accuracy requires validation through FISH or NGS techniques.
For advanced or recurrent gastric cancer cases unresponsive to standard treatment, conducting tests to detect markers such as Claudin 18.2, fibroblast growth factor receptor 2 (FGFR2), and cellular‐mesenchymal‐epithelial transition (c‐MET) [34] can help identify potential therapeutic targets.