Immunohistochemistry can be useful in diagnosing bone and soft tissue sarcomas. In bone tumours the decalcification process can destroy antigens in the tumour cells and this can limit the usefulness of the technique. As with all tumours the following general points must be emphasised:

• antibodies are not specific to a particular type of tumour, there is often overlap with several other types.

• immunohistochemistry will not directly determine if the tumour is benign or malignant.

• beware of interpretation in the presence of extensive tumour necrosis.

• be careful of edge artefact.

• know whether the antibodies you use should stain on the membrane, within the cytoplasm or nucleus of the cell.

• always use a panel of antibodies.

The use of immunohistochemistry in bone and soft tissue sarcomas is a huge subject and good standard textbooks of soft tissue tumour pathology should be consulted. However, the list below is a very simplified version illustrating some of the uses of the more common antibodies: LCA (CD45)

• lymphomas, chronic inflammation. Cytokeratins

• metastatic carcinoma, synovial sarcoma, epithelioid sarcoma. PRAP/PSA

• metastatic prostate carcinoma. S100

• neural, lipomatous and cartilaginous tumours. Smooth muscle actin

• muscle tumours, fibroblastic and myofibroblastic soft tissue lesions. Desmin

• Ewing's sarcoma but it can be positive in many other tumours.

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