Primary Orbital Apocrine Adenocarcinoma: A Rare Case Concomitant with Gastric Adenocarcinoma

Purpose: To report a case of primary orbital apocrine adenocarcinoma in a patient diagnosed with gastric adenocarcinoma.Case summary: A 43-year-old male patient diagnosed with gastric adenocarcinoma 3 months prior presented with a gradually enlarging mass in the lower medial aspect of the left eye for 1 year. At initial examination, his best-corrected visual acuity was 1.0 in both eyes and slit-lamp examination revealed no abnormalities. The left eye exhibited proptosis with restricted adduction, abduction, and depression. Orbital magnetic resonance imaging revealed an irregularly shaped mass measuring 56 × 46 × 38 mm in the left inferomedial orbit, invading the medial and inferior rectus muscles. Histopathological analysis of the orbital tumor revealed abundant eosinophilic cytoplasm. Immunohistochemical staining was positive for androgen receptor, and gross cystic disease fluid protein-15, both of which were negative in the gastric adenocarcinoma tissue. Additionally, the mucin phenotypes observed differed from those in the gastric cancer tissue. Based on these findings, the patient was diagnosed with primary orbital apocrine adenocarcinoma.Conclusions: Primary orbital apocrine adenocarcinoma is an extremely rare malignant tumor. In patients with gastric cancer, malignant tumors in the orbit can arise as either primary neoplasms or metastatic lesions. Therefore, accurate diagnosis through immunohistochemical staining is essential to determine the appropriate treatment approach.