LAUSR

e16105 Background: Gastric cancer (GC) and gastroesophageal junction cancer (GEJ) are the second most prevalent and lethal digestive malignancies worldwide. According to GLOBOCAN 2020, the incidence in Mexican population is 4.5% and represents 7% of all deaths. In GC and GEJ, the frequency of HER2 overexpression varies widely in the literature. Actually the blocking anti-HER2 is the standard therapy in GC and GEJ with overexpression HER2 according to the ToGa Trial. There are few studies that describe this population in mexican patients. Methods: We conducted a retrospective, observational analysis. Medical records of patients with GC or GEJ cancer from January 2015 to January 2021 were reviewed. A total of 91 patients were retrieved from the pathology database. Clinicalpathologic features collected were sex, age, pTNM stage (AJCC 8th edition), histology type, HER-2 status, metastases sites and treatment. The HER-2 determination was performed in all cases with immunohistochemistry (IHQ). Results: We found 10 patients with GC and GEJ with HER-2 overexpression by IHC, five patients with FISH positive and 2 of them with amplification by next generation sequence (FoundationOne). The median age was 56.9 years (27-68). There were more male patients (n = 8) than female patients (n = 2), with male/female ratio of 4:1. 8 patients had performance status (PS) 0 or 1, and the rest PS 2. The primary site was gastric carcinoma in 3 patients, and in 7 the tumor was located in GEJ. The clinical stage at diagnosis in 7 patients was metastatic, and 3 locally advanced. The most common sites of metastasis were lung (n = 5), liver (n = 4), and pleural, bone and central nervous system (each one with one patient). Intestinal-type GCs were most prevalent with 8 patients, and the rest were diffuse and signet ring cells. All patients received anti-HER2 blockade, 6 in the first line therapy, and 4 patients in the second line or more. Regarding the backbone regimen of the trastuzumab based therapy, fluoropyrimidine/platinum were the mainstay in 9 patients, and 1 with platinum and taxane scheme. Median number of cycles of trastuzumab was 8 (range, 4-24). The tumor responses were as follows: complete response (CR) 10%, partial response (PR) 30%, stable disease 50% and progressive disease 1 patient. The median progression-free survival was 6.6 months (1.3-23.1 months), and a median of overall survival was 21 months (6.4-51.5 months). The most frequently reported adverse events were diarrhoea in 3 patients (all grade 2), and mucositis in 1 patient. Cardiac adverse events were not reported. Conclusions: In our cohort, the prevalence of HER2 overexpression by IHC was 11%. In previous reports, the most important ToGa trial, 22% of the patients with metastatic GC and GEJ were HER2 positive. The PFS and OS in ToGa trial were 13.8 and 17.1 months respectively. By comparison our cohort the PFS and OS in ToGa trial were 6.6 and 21 months.