Abstract
Perioperative chemotherapy is standard treatment for patients with early high-risk gastroesophageal adenocarcinoma independent of molecular subtype. Approximately 8% of gastroesophageal cancers have a microsatellite instable phenotype (MSI-H), and retrospective analyses of neoadjuvant/adjuvant chemotherapy trials suggests no survival benefit in this patient population compared with surgery alone. Patients with advanced MSI-H malignancies obtain durable responses with immunotherapy using anti-programmed cell death protein 1 (PD-1) checkpoint blockade. We describe a case of a patient with an early MSI-H gastroesophageal adenocarcinoma who progressed on neoadjuvant chemotherapy precluding subsequent surgical resection. The patient was subsequently treated with immunotherapy using the anti-PD-1 antibody nivolumab and the anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) antibody ipilimumab leading to a complete remission with biopsies of the residual tumor mass and regional lymph nodes revealing no residual tumor. This case highlights the lack of benefit from neoadjuvant chemotherapy in patients with MSI-H gastroesophageal cancers and suggests that perioperative anti-PD-1-based immunotherapy should be further investigated in this patient population. KEY POINTS: This report describes the successful salvage treatment of a patient with an early high-risk MSI-H gastroesophageal carcinoma who progressed through neoadjuvant chemotherapy using combination immunotherapy of the anti-programmed cell death protein 1 (PD-1) antibody nivolumab and the anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) antibody ipilimumab, leading to an ongoing complete remission. The case is in keeping with retrospective analyses of perioperative treatment trials demonstrating a lack of chemotherapy benefit in patients with MSI-H gastroesophageal carcinoma and supports the further investigation of anti-PD-1-based immunotherapy as a treatment modality in this patient population. The case highlights the potential difficulties that may be encountered in the surgical management of patients treated with neoadjuvant immunotherapy with reactive dense fibrotic changes precluding surgical resection.