Dentine matrix protein 1 (DMP-1) is a marker of bone formation and mineralisation in soft tissue tumours

Dentine matrix protein 1 (DMP-1) is a non-collagenous matrix protein found in dentine and bone. It is highly expressed by osteocytes and has been identified in primary benign and malignant osteogenic bone tumours. Bone formation and matrix mineralisation are seen in a variety of benign and malignant soft tissue tumours and tumour-like lesions, and in this study, we analysed immunohistochemically the DMP-1 expression in a wide range of soft tissue lesions (n = 254) in order to assess whether DMP-1 expression is useful in the histological diagnosis of soft tissue tumours. Matrix staining of DMP-1 was seen in all cases of myositis ossificans, fibro-osseous tumour of the digits, extraskeletal soft tissue osteosarcoma and in most cases of ossifying fibromyxoid tumour. DMP-1 was also noted in dense collagenous connective tissue of mineralising soft tissue lesions such as tumoural calcinosis, dermatomyositis and calcific tendinitis. DMP-1 was expressed in areas of focal ossification and calcification in synovial sarcoma and other soft tissue tumours. With few exceptions, DMP-1 was not expressed in other benign and malignant soft tissue tumours. Our findings indicate that DMP-1 is a matrix marker of bone formation and mineralisation in soft tissue tumours. DMP-1 expression should be particularly useful in distinguishing extraskeletal osteosarcoma and ossifying fibromyxoid tumour from other sarcomas and in identifying areas of osteoid/bone formation and mineralisation in soft tissue tumours.