SOLITARY FIBROUS TUMOR - SIGNIFICANCE OF P53 AND CD34 IMMUNOREACTIVITY IN ITS MALIGNANT TRANSFORMATION

Aims: To clarify the association of p53 and CD34 expression with devel opment of malignant solitary fibrous tumour we have studied 10 cases o f solitary fibrous tumour arising in the pleura, retroperitoneum and p elvic cavity with clinicopathological features of malignancy, Methods and results: Tumours were localized solid masses with or without necro sis in eight and they nearly totally occupied the pleural cavity in tw o. Basic histology of the tumours was the proliferation of spindle cel ls arranged in 'patternless' pattern or in interlacing bundles with nu clear atypia and mitotic activities of various degree. In two, high-gr ade foci were present within low or intermediate-grade tumours, Recurr ent tumours also showed more atypical features than primary tumours in two, Immunohistochemical studies showed CD34 positivity in seven, but three of them showed marked diminution or complete loss of CD34 expre ssion in high-grade foci or a recurrent tumour. Three high-grade cases showed totally negative staining for CD34. p53 was strongly expressed in cases with fatal outcome, clinical recurrence, nuclear atypia, hig h mitotic activity or local invasion, whereas almost negative in benig n tumours, Conclusions: Malignant solitary fibrous tumours may occur d e novo or by transformation within benign or low-grade tumours and may be associated with p53 mutation. Although CD34 is a useful marker in the diagnosis of solitary fibrous tumour, one should bear in mind that its expression can be lost in high-grade tumours.