[Sarcomatous degeneration in Paget disease of bone. Apropos of a clinical case].

Sarcomatous degeneration is the most dreaded complication of Paget's disease of bone: this case report offers an opportunity for underlining the difficulties of differential diagnosis in a case of pulmonary metastatization in the presence of osteitis deformans. Immunohistochemical assay applied to the cytology of pulmonary needle-aspiration and surgical biopsy targeted to the suspected neoplastic lesion allowed correct diagnosis. This case confirms the very poor prognosis of this kind of neoplasm: the rapidity of the fatal outcome was not significantly influenced even by the most aggressive polychemotherapy. This poor prognosis appears to be related to a more aggressive growth of the neoplasm and to the reduced immunologic resistance of the elderly.