P53 and Rb immunohistochemistry staining reveal subtypes of gastric neuroendocrine carcinoma with distinct prognosis.

Abstract

e16210 Background: Due to the rarity, research on gastric neuroendocrine carcinoma (NEC) is limited. The treatment has been extrapolated from small-cell lung cancer (SCLC) data. However, a previous study found gastric NECs had a genetic feature characterized by a lower frequency of RB1 mutations than SCLC. Several studies also showed RB1mutation or loss of Rb expression could predict the efficacy of SCLC treatment in NEC. Our study investigated a subtyping method by p53 and Rb immunohistochemistry (IHC) staining in gastric NEC, which might help identify patients responding to SCLC treatment. Methods: Patients with gastric NEC who underwent radical surgery in Peking Union Medical College Hospital (PUMCH) from 2013 to 2021 were identified. The expression of Rb, p53, PD-L1 and CD8 T cell infiltration were accessed by IHC stain. The mutations of RB1 and TP53, tumor mutation burden (TMB), and microsatellite instability (MSI) were detected by whole-exom sequencing (WES). Fisher’s exact test and Mann–Whitney test were used to detect differences between groups. Spearman's test was used to detect correlations between variables. Kaplan-Meier and Cox hazards methods were applied to the survival analysis. Samples of gastric adenocarcinoma, gastric neuroendocrine tumor (NET), and SCLC were also included. Results: A total of 41 patients with gastric NEC were included. WES was carried out in 28 patients. TP53 mutation was detected in 14 patients. RB1 mutation was detected in 1 patient. A classification method based on gene mutation was not able to be further investigated. In IHC of 41 patients, 46.2% showed Rb expression absence. 68.4% had abnormal p53 expression. 39 patients were classified based on IHC results. Patients with both abnormal expression of p53 and Rb were defined as SCLC-like type, accounting for 38.5%.The remaining patients were defined as non-SCLC-like type. SCLC-like gastric NEC had an increased number of lymph nodes metastasis (P = 0.001) and higher TNM stage (P < 0.001). The SCLC-like group's overall survival (OS) was significantly lower than the non-SCLC-like group (P = 0.023). Classification based on p53 and Rb expression was an independent predictor of OS (P = 0.021), HR = 4.690, 95%CI (1.263, 17.421). The classification results of gastric NEC were significantly different from those in gastric NET(P = 0.001), gastric adenocarcinoma(P = 0.002), but not in SCLC(P = 0.464). In 39 classified patients, the positive rate of PD-L1 expression was 23.1%; CD8 T cells high infiltration (>25 % of the stromal area) was 46.7%; the median TMB was 4.9 Muts/MB, and MSI was not detected. There was no significant difference in the expression of immunotherapy-related markers between the two types. Conclusions: Our study revealed subtypes of gastric NEC based on p53 and Rb expression with different prognoses. Further research on the treatment efficacy predictive role of this subtyping method is warranted.