Immunotherapy and Tumor Heterogeneity in Advanced Goblet Cell Adenocarcinoma of the Appendix: A Case Report

Goblet cell adenocarcinoma (GCA) of the appendix is a rare and aggressive malignancy, often presenting with peritoneal dissemination. Treatment typically involves surgical resection and chemotherapy, though the management of metastatic disease remains complex and with no clear guidelines. We present a case of advanced GCA with extensive peritoneal involvement in a 66-year-old woman, in which repeated molecular testing led to the identification of a clone with high microsatellite instability, guiding the successful use of immunotherapy. Additionally, molecular profiling via liquid biopsy played a key role in subsequent treatment decisions. This personalized treatment approach resulted in a survival period of 42 months, which is nearly double the median overall survival (mOS) for this condition. The patient's journey highlights the importance of personalized medicine, illustrating how continuous molecular monitoring and adaptability to emerging data can significantly improve outcomes in patients with tumors exhibiting molecular heterogeneity. PEER REVIEWED ARTICLE Peer reviewers: Dr Thibaud Kössler, Geneva University Hospital, Geneva, Switzerland One anonymous peer reviewer Received on December 5, 2024; accepted after peer review on December 20, 2024; published online on December 27, 2024.