S3185 Immunohistochemical Profiling of PD-L1 and HER-2 in Latin American Gastric Cancer Patients

Introduction: The expression of programmed death-ligand 1 (PD-L1) and human epidermal growth factor receptor 2 (HER-2), in gastric cancer has been associated with high mortality rates and short overall survival periods, emphasizing the importance of their early identification for timely selection of appropriate treatments. Methods: Descriptive observational study of a retrospective cohort of patients with up to 5 years of follow-up, diagnosed with advanced-stage gastric cancer and treated at an oncology center in Bogotá, Colombia. Additionally, these patients underwent immunohistochemical testing for the detection of PD-L1 and HER-2. The objective of this study is to determine the frequency of expression of the PD-L1 and HER-2 biomarkers in a sample of Colombian patients. A univariate analysis was conducted to determine and compare the frequency of HER-2 and PD-L1 expression in Latin American patients with advanced gastric cancer. Results: One-hundred fifty-five patients diagnosed with gastric cancer were included, of which 58% were men. Histologically, 90% corresponded to adenocarcinoma, predominating in men. Forty-seven percent were poorly differentiated, 21% exhibited signet ring cells, and 11% showed tubular pattern. PD-L1 positivity was observed in 27%, with 61% being men; 58% combined positive score (CPS) >10, 22% CPS 5-9, and 17% CPS 1-4. HER-2 positivity was detected in 7%, with 5% being men of the total patient pool. Two percent of patients had a positive result for HER-2 and PD-L1. Follow-up was conducted on 22% of patients over a 60-month period, with an overall survival (OS) of 22.2 months and a progression free survival (PFS) of 6.6 months. Eighteen percent presented involvement of adjacent tissues, 9% cervical lymph node involvement, and 6% peritoneal involvement. Immunotherapy was administered to 35% of patients; 17% deceased, with an OS mean of 21.7 months and a PFS of 6.5 months. For the group of patients receiving chemotherapy alone, 41% deceased, with an OS mean of 22.5 months and a PFS mean of 6.7 months. Conclusion: PD-L1 expression affects approximately one quarter of the Colombian population, while HER-2 expression is infrequent in our population. Immunotherapy and chemotherapy exhibited similar overall survival means; however, the use of chemotherapy alone was associated with a higher number of deaths.