[Tumoral hypophosphoremic osteomalacia]

Various tumoral diseases may induce hypophosphataemic osteomalacia. This is the case, in particular, with mesenchymal tumours and sclerosing metastases of prostatic cancer; much less common causes are diffuse connective tissue dysplasias and non-prostatic epitheliomas. Depending on whether osteomalacia results from a mesenchymal tumour or from osteitis of prostatic origin, the practical problems encountered are quite different. In the first case, the important point is not to miss a mesenchymal tumour when confronted with an acquired and apparently idiopathic hypophosphataemia; repeated examinations at regular intervals are sometimes necessary to detect the tumour which is usually benign; osteomalacia can then be cured by its removal. In the second case, the difficulty is to detect an osteomalacia which may be masked by bone metastases and to recognize its tubular origin in order to prescribe the appropriate treatment. Little is known about the pathogenesis of tumoral hypophosphataemic osteomalacia. The renal diabetes and low 1,25 (OH)2 D plasma levels frequently associated with the disease reflect a complex enzymatic disorder thought to be caused by a humoral mediator secreted by the tumour. Studies carried out in this field have already shown that 1,25 (OH)2 D is therapeutically useful when the tumour cannot be excised.