Tumour-to-tumour metastasis: head and neck squamous cell carcinoma to enchondroma.

Metastatic disease is a common occurrence in malignancy with certain cancers recognised to have a high incidence of metastases, particularly the liver, lungs, and bones. Tumour-to-tumour metastases are an exceptionally rare occurrence, where a distant malignancy metastasises to a secondary distinct tumour. Breast and lung carcinomas are the more commonly reported origin sites, whilst renal cell carcinomas and meningiomas are the most reported recipient malignant and benign tumours respectively. In this article, we describe an unusual case of a metastatic head and neck squamous cell carcinoma (HNSCC) complicated by tumour-to-tumour metastasis to a benign intramedullary cartilage lesion in the distal femur.