Tumour-to-tumour metastasis: breast carcinoma to an olfactory neuroblastoma.

Tumour-to-tumour metastasis is a rare phenomenon. It occurs when a primary tumour is a recipient of a separate tumour within the same individual. We present a case of a 66-year-old woman with known breast cancer who presented with one-sided nasal symptoms. Examination and imaging revealed a unilateral polyp arising from the skull base. She underwent endoscopic polypectomy with the histology demonstrating tumour-to-tumour metastasis from a breast carcinoma to an olfactory neuroblastoma, a rare sinonasal tumour. Clinicians should be cautious of distant metastases in any patient presenting with head and neck symptoms and a known primary tumour. This is the first documented case of this type.