Pathological complete response after neoadjuvant immunochemotherapy in gastric cancer with microsatellite instability without PD-L1 expression (CPS = 0). A case report

Despite the use of modern treatment methods for gastric cancer (GC), survival rates in locally advanced stages remain unsatisfactory. This necessitates the search for new therapeutic options and potential predictive factors for tailoring treatment approaches. The emergence of new molecular classifications like The Cancer Genome Atlas (TCGA) and the Asian Cancer Research Group (ACRG), leading to the identification of a distinct subset — gastric cancer with high microsatellite instability (MSI-H) caused by mismatch repair deficiency (dMMR), has paved the way for a novel treatment direction: immunotherapy. MSI status and PD-L1 expression are regarded as predictors of immunotherapy efficacy in GC. However, the question of which marker is more accurate or if they should be considered together remains unanswered. Furthermore, the efficacy of checkpoint inhibitor therapy is often attributed to increased PD-L1 expression in microsatellite unstable tumors compared to microsatellite stable ones. The article discusses a case demonstrating the high efficacy of immunochemotherapy, resulting in complete pathomorphological regression of the tumor in a patient with locally advanced gastric cancer and MSI-H status after neoadjuvant immunochemotherapy, despite the absence of PD-L1 expression (CPS-0). The patient has been monitored for 1.5 years post-treatment at the N. N. Blokhin National Medical Research Center of Oncology without signs of progression.

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