Primary Orbital Mucinous Adenocarcinoma: A Malignancy With Rapid Metastasis.

Primary mucinous adenocarcinoma of the orbit is an exceptionally rare epithelial malignancy that closely mimics metastatic disease both clinically and radiologically, often delaying definitive diagnosis. We report the case of a 69-year-old man who presented with progressive ocular pain, axial proptosis, and a well-circumscribed orbital mass on imaging. Histopathological evaluation following incisional biopsy revealed a mucinous adenocarcinoma with signet ring morphology. Immunohistochemical analysis demonstrated strong cytokeratin 7 (CK7) positivity and weak CK20 expression, favoring a primary orbital origin. Comprehensive systemic evaluation failed to reveal a primary tumor elsewhere, supporting the diagnosis of a primary orbital neoplasm. Despite early intervention, the tumor exhibited rapid metastatic progression, and the patient died within six weeks of diagnosis. This case highlights the aggressive clinical course and diagnostic complexity of primary orbital mucinous adenocarcinoma, underscoring the need for high clinical suspicion, prompt biopsy, and a multidisciplinary approach, although prognosis remains dismal.