[Clinicopathological and molecular diagnostic features of early-onset gastric cancer: a study based on data from a single-center dedicated gastric cancer database]

Objective: To clarify the clinicopathological, especially molecular, features of early-onset gastric cancer with the aim of informing analysis of treatment strategies. Methods: In this retrospective case-control study, we examined data from a dedicated gastric cancer database in Zhongshan Hospital affiliated to Fudan University. The original cohort comprised 2506 patients with gastric cancer who had undergone gastrectomy in Zhongshan Hospital Fudan University from July 2020 to October 2021, including 198 with early-onset gastric cancer (aged ≤45 years) and 2,308 with non-early gastric cancer. We used a simple random sampling method to select 396 of the 2,308 patients aged >45 years (ratio of 1:2) as the control group and then compared molecular diagnostic data and clinicopathological features of the two groups. Results: The median age was 39 years in the early-onset gastric cancer group, while 66 years in the control group. The clinicopathological features of early-onset gastric cancer included female predominance (59.1% [117/198] vs. 27.8% [110/396], χ²=54.816, P<0.001), less comorbidity (32.3% [64/198] vs. 57.1% [226/396], χ²=32.355, P<0.001), poorer differentiation (93.9% [186/198] vs. 74.5% [295/396], χ²=30.777, P<0.001) and higher proportion of diffuse type (40.4% [80/198] vs. 15.9% [63/396], χ²=69.639, P<0.001), distant metastasis (7.1% [14/198] vs. 2.8% [11/396], χ²=6.034, P=0.014). Regarding treatment, distal gastrectomy was more commonly performed than proximal gastrectomy (55.1% [109/198] vs. 47.0% [186/396], 1.5% [3/198] vs. 8.3% [33/396], χ²=11.644, P=0.003). Family history of gastric cancer, TNM stage, tumor size, lymph node dissection, nerve invasion, nodes harboring metastases, range of lymph node dissection, digestive tract reconstruction procedure, implementation of laparoscopic surgery, combined resection, and preoperative treatment did not differ significantly between the two groups (all P>0.05). Molecular diagnosis showed there was a smaller percentage of mismatch repair deficiency in the early-onset gastric cancer than in the control group (1.0% [2/198] vs. 10.1% [40/396], χ²=16.301, P<0.001), and a higher rate of positivity for Claudin 18.2 (77.8% [154/198] vs. 53.0% [210/396], χ²=5.442,P<0.001). HER-2 and Epstein-Barr virus positivity rates did not differ significantly between the two groups. Conclusion: Early-onset gastric cancer is a distinct type of gastric cancer with a high degree of malignancy, and treatment targeting Claudin 18.2 may be effective.