A Rare Case of Appendiceal Goblet Cell Adenocarcinoma Complicated by Development of a Loculated Pleural Effusion.

Appendiceal goblet cell adenocarcinoma (GCA) is a rare malignancy that often presents as acute appendicitis. We present a 57-year-old woman with a history of breast cancer who presented with right lower quadrant pain, fever, nausea, and vomiting and underwent appendectomy for presumed uncomplicated appendicitis. She was discharged postoperatively, and final pathology subsequently revealed GCA of the appendix. Approximately one week later, she returned with dyspnea and was found to have a new, multiloculated, exudative pleural effusion. Pleural fluid cytology was negative for malignancy. She required chest tube placement with intrapleural fibrinolytics followed by surgical decortication for definitive management. Given recent surgeries and concern that early positron emission tomography/computed tomography (PET-CT) would be confounded by postoperative inflammation, a multidisciplinary decision was made to initiate systemic chemotherapy prior to right hemicolectomy. She later underwent hemicolectomy with a favorable outcome and no evidence of peritoneal metastasis. This case highlights an unusual extraperitoneal manifestation of appendiceal GCA and an individualized treatment sequence differing from standard management, underscoring the need for further study of optimal treatment sequencing and surveillance strategies.