ESR1 and aneurysmal bone cyst: Baseline characteristics such as age, prior endocrine therapy and ER/PgR expression were not different between the two groups when retrospectively analysed; this also holds true for laboratory values such as haemoglobin (Hb), white blood cell count (WBC) and alkaline phosphatase (ALP), which have been shown to be prognostic for OS in ABC [9].