SUMMARY: Feminizing estrogen-secreting adrenocortical carcinomas (ACCs) are exceedingly rare and carry a poor prognosis. The most common presenting trait is gynecomastia, but enlarged breasts are also a frequent clinical finding in healthy men. Biochemical evaluation may be challenging. As such, there is a high risk of delayed diagnosis and treatment opportunity. Here, we present a case with an estrogen-producing ACC where the abnormal steroid profile obtained at the time of initial workup was essential for the prompt diagnosis. Wider adoption of liquid chromatography mass spectrometry-based steroid assays has potential to improve early diagnosis of feminizing estrogen-secreting ACC. LEARNING POINTS: Feminizing estrogen-secreting adrenocortical carcinomas (ACCs) are a rare, but an important differential diagnosis in men with rapidly developing gynecomastia. Biochemical evaluation is essential for a prompt diagnosis. Steroid hormone profiling using liquid chromatography mass spectrometry technology has the potential to improve early diagnosis of feminizing estrogen-secreting ACC.
