Tumour induced osteomalacia: a report of two cases. A disease of defective matrix synthesis?

Tumour induced hypophosphataemic osteomalacia or rickets is a well delineated clinical entity. There is confusion, however, about the nomenclature and classification of the associated tumours. The tumour factor responsible for the biochemical abnormalities has also not been identified. We report here two cases: one, a 43 year old male with a soft tissue tumour in the left vastus medialis, and the other, a 25 year old female with a soft tissue tumour in the right anterior axillary fold. Reversal of biochemical abnormalities and clinical improvement occurred after removal of the tumour in both cases. Both tumours showed unusual morphology characterised by spindle cell component, large vascular spaces, osteoclast-like giant cells, calcification and ossification. The tumour in the second patient was benign, while the nature of the tumour in the first patient was debated. We speculate that defective matrix may be the cause of unusual histology of the tumours, and also the source of the phosphaturic factor.