Adrenal cortical carcinoma (ACC) is an extremely rare disease with a variable prognosis. Current prognostic markers have limitations in identifying patients with a poor prognosis. Herein, we aimed to investigate the prognostic protein biomarkers of ACC using mass-spectrometry-based proteomics. We performed liquid chromatography-tandem mass spectrometry (LC-MS/MS) using formalin-fixed paraffin-embedded (FFPE) tissues of 45 adrenal tumors.