Metastatic breast cancer presenting as a primary hindgut neuroendocrine tumour.

The examination of limited, potentially non-representative fragments of tumour tissue from a core biopsy can be misleading and misdirect subsequent treatment, especially in cases where a primary tumour has not been identified. This case report is of a 65-year-old woman presenting with a destructive sacral mass, diagnosed on radiological imaging and core biopsy as a hindgut neuroendocrine tumour, which on histopathological review of the subsequently resected tumour was found instead to represent a metastasis from an occult hormone-positive breast cancer with neuroendocrine features.