| Summary: | Hereditary diffuse gastric cancer (HDGC) is a rare malignancy characterized by autosomal dominant inheritance of pathological variants of the CDH1 gene encoding E-cadherin, which is involved in cell–cell adhesion, maintenance of epithelial architecture, tumor suppression, and regulation of intracellular signaling pathways. Late-stage recognition of HDGC is typically associated with a poor clinical outcome due to its metastatic potential and risk of lobular breast cancer (LBC) development. The American College of Gastroenterology issued guidelines to evaluate HDGC, test for CDH1 genetic variants, and recommend prophylactic gastrectomy for carriers of CDH1 mutations. If surgery is not pursued, endoscopy is a surveillance alternative, although it carries a limited ability to detect malignant foci. As part of clinical research efforts, novel endoscopy advances are currently studied, and a center of excellence for HDGC was created for a comprehensive multidisciplinary team approach. Within this review, we cover current conventional treatment modalities such as gastrectomy and chemotherapy, as the mainstay treatments, in addition to Pembrolizumab, an immune checkpoint inhibitor, as the last therapeutic resort. We also shed light on novel and promising approaches with emphasis on immunotherapy to treat HDGC. We further break down the therapeutic paradigms to utilize molecular tools, antibodies against checkpoint inhibitors, TGF-β and tyrosine kinase inhibitors, cell-based adoptive therapies, and oncolytic viral therapies. We aim to expand the understanding on how to modulate the tumor microenvironment to tip the balance towards an anti-tumor phenotype, prevent metastasis of the primary disease, and potentially alter the therapeutic landscape for HDGC.
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