Dear editor

We have recently observed a case of orbital myxoid solitary fibrous tumour (SFT), found in the right eye of a 29-year-old woman. The diagnosis was confirmed by Christopher D.M. Fletcher, Professor of Pathology at Harvard Medical School and Brigham and Women’s Hospital, USA. We read with great interest Yin W. and colleagues’ article “A primary atypical solitary fibrous tumour of the sella mimicking non-functional pituitary adenoma: a case report”, published online in Acta Neurochirurgica in June 2009 [2]. These authors wrote that “according to the immunohistochemical examination, the diagnosis of atypical SFT was established”. In the volume World Health Organization Classification of Tumour of Soft Tissue, “atypical SFT” is not reported, but SFTs are classified as benign or malignant [1]. The atypical variant is not included in the classification. World Health Organization classification reports that “tumours cells in SFT are characteristically immunoreactive for CD34 (90-95% of cases) and CD99 (70%). Twenty to thirty-five percent of them are also variably positive for epithelial membrane antigen, BCL2, and smooth muscle actin. Focal and limited reactivity for S100 protein, cytokeratins, and/or desmin has also occasionally been reported”. The less intense immunoreactivity for CD34 may be considered into the 5-10% CD34-negative SFTs. However, it should not be accepted as the conclusive feature for defining a new SFT histotype (c.d. “atypical SFT), other than the malignant and benign variants.