Glomus tumour of uncertain malignant potential.

A 71-year-old man presented with a several year story of a slowly enlarging, painful mass of the knee. Surgical findings showed a subcutaneous, well-circumscribed mass fixed to the patella, and a wide resection was performed. Macroscopically, the tumour measured 6 x 5 x 5 cm and was well circumscribed. The tumour was characterised by superficial location, large size and focal marked atypia. In addition, areas of benign glomus tumour (GT) were identified. The findings appear to be consistent with the diagnosis of GT of uncertain malignant potential.