Oncogenic osteomalacia associated with a mesenchymal chondrosarcoma.

A patient with phosphaturic osteomalacia without chemical or pathological evidence of hyperparathyroidism and subnormal urinary cyclic AMP excretion was treated with vitamin D and phosphates for 9 months with partial improvement of osteomalacia, but not phosphaturia. Subsequent removal of a mesenchymal chondrosarcoma of the foot led to prompt resolution of phosphaturia and healing of the osteomalacia. Although 1,25-dihydroxyvitamin D levels were not obtained before vitamin D therapy, the levels noted during continued severe phosphaturia preoperatively were not lower than those obtained several months postoperatively during the healing phase. Studies done 1 year after tumor removal showed normalization of phosphaturia, urinary cyclic AMP, and bone histology. We suggest that the tumor elaborated products which promoted nonparathyroid mediated phosphate excretion independently from any effects on vitamin D metabolism.