Quantitative measurements of desmin and vimentin immunostains and cell density in leiomyomas and leiomyosarcomas.

The distinction between benign and malignant smooth muscle tumours relying on histological features such as the mitotic index and pleomorphism remains a generally acknowledged difficulty in modern pathology. A cell image processor was therefore used to quantitatively assess the desmin and vimentin immunostain in 39 smooth muscle tumours which included 26 benign (leiomyomas) and 13 malignant (leiomyosarcomas) cases. The 13 leiomyosarcomas were primary (non-recurrent and non-metastatic). Ploidy level and cell density were also assessed on each of these 39 tumours by means of the computer-assisted microscopic analysis of 5-microns thick Feulgen-stained histological sections. The results show that while neither the ploidy level determination nor the quantitative assessment of the vimentin immunostain made it possible to distinguish between leiomyomas and leiomyosarcomas, cell density determination and the quantitative assessment of the desmin immunostain enabled such a distinction to be made. Indeed, the leiomyomas exhibited a much higher level of desmin positivity than the leiomyosarcomas, as did diploid tumours as compared to the aneuploid (benign or malignant) ones. Furthermore, the leiomyoma group exhibited a significantly lower mean cell density value than the leiomyosarcoma group. The present study further confirms the lack of relationship between ploidy level and cytological malignancy in smooth muscle tumours.