The Role of Immunohistochemistry in Distinguishing Smooth MuscleTumours from Mesenchymal Tumours with Myoid Differentiation

Overview

The expression of alpha smooth muscle actin, muscle specific actin, desmin, h-caldesmon, andcalponin was studied immunohistochemically in the following soft tissue and bone tumours andtumour-like lesions: muscle fibromatosis, inflammatory pseudotumours, chondroblastoma, enchondroma,chondrosarcoma, fibrous dysplasia, ossifying myositis, osteoblastoma, convential osteosarcoma,leiomyoma and leiomyosarcoma. Tumours and tumour-like lesions withmyofibroblastic cells, osteoblasts and chondroblasts frequently exhibited intensive immunoreactivityfor the muscle markers, and therefore, some of them may occasionally be confused withleiomyoma and leiomyosarcoma. Calponin does not help to differentiate various mesenchymaltumours expressing muscle markers, because it also stains intensively myofibroblasts, osteoblastsand chondroblasts. We confirmed that h-caldesmon was expressed intensely in leiomyomas andleiomyosarcomas, and never in the other tumours examined, with the exception of three chondroblastomas.The results have shown that h-caldesmon is a rather specific and sensitive markerfor smooth muscle tumours, but it can also stain some actin positive myochondroblasts. It ispossible that the positivity of h-caldesmon in some chondroblastomas is due to their completemyogenic transdifferentiation, and so we use the term myochondroblasts and myochondrocytesfor designation of such S-100 protein, actin, and h-caldesmon positive cells.

Key words:
actin – calponin – h-caldesmon – mesenchymal tumours – bone – soft tissue – myochondroblasts