Chapter 1 – Pathology and Classification
WHO classification of soft tissue sarcomas: use of immunohistochemistry
In addition to histological features, immunohistochemistry (IHC) is used to determine line of differentiation in STS.
The different markers have different sensitivity and specificity.
Diffuse nuclear MyoD1 staining in case of rhabdomyosarcoma (RMS) indicates rhabdomyogenic differentiation.
Usually a panel of immunohistochemical markers is used.
Examples of second-line markers that are more specific include mucin 4 (MUC4) for low-grade fibromyxoid sarcoma/sclerosing epithelioid fibrosarcoma, loss of H3K27me3 in malignant peripheral nerve sheath tumour and ETV4 in CIC-rearranged round cell sarcoma.
Strong membranous staining of vascular marker CD31 in case of epithelioid angiosarcoma indicates endothelial differentiation.
IHC can also be used as a surrogate to identify specific molecular alterations.
Examples include nuclear staining of STAT6 in solitary fibrous tumour, loss of INI1 in epithelioid sarcoma, nuclear CAMTA1 in epithelioid haemangioendothelioma and TFE3 in alveolar soft part sarcoma (ASPS).
IHC is used to detect MDM2 amplification in well-differentiated/dedifferentiated liposarcoma. Amplification can be confirmed using fluorescent in situ hybridisation (FISH).
REVISION QUESTIONS
1. What is the purpose of IHC in STSs?
2. Which markers are used to demonstrate endothelial differentiation?
3. Which tumour is characterised by amplification of MDM2?
Classification of soft tissue sarcomas Classification of STS: histological grading
