Primary adrenal small cell neuroendocrine carcinoma in a patient with sarcoidosis and synchronous colon adenocarcinoma

Primary adrenal neuroendocrine carcinoma (NEC), particularly the small cell subtype, is exceptionally rare. In patients with sarcoidosis, inflammatory lymphadenopathy may mimic a metastatic disease, making disease detection difficult. A 76-year-old man with sarcoidosis was referred for an enlarging left adrenal incidentaloma that had increased in size from 7 mm to 19 × 14 mm over 3 years. Hormonal evaluation revealed unremarkable findings; laparoscopic adrenalectomy was performed because malignancy could not be excluded. Histopathological examination revealed small cell NEC with positive synaptophysin and chromogranin A staining, and a Ki-67 labeling index of 80%. One month after surgery, para-aortic lymphadenopathy was detected. Fluorodeoxyglucose positron emission tomography/computed tomography (CT) showed uptake in the para-aortic lymph nodes and ascending colon, where colonoscopy identified synchronous adenocarcinoma. The cause of the lymphadenopathy was uncertain because of coexisting sarcoidosis and colon cancer. Cisplatin plus irinotecan induced a partial response; however, disease progression was observed. CT-guided lymph node biopsy confirmed metastatic NEC. Second-line amrubicin therapy reduced tumor size; comprehensive genomic profiling revealed a tumor mutation-burden-high phenotype. This case highlights diagnostic challenges in the evaluation of lymphadenopathy in patients with sarcoidosis and synchronous malignancy, emphasizing the importance of pathological confirmation for guiding appropriate management.