Primary cardiac sarcomas may develop from resident or bone marrow‐derived mesenchymal stem cells: use of immunohistochemistry including CD44 and octamer binding protein 3/4

AIMS: To provide evidence that cardiac sarcomas 'not otherwise specified' express markers that might indicate their cellular origin or identify any lines of differentiation. METHODS AND RESULTS: We reviewed all 11 cases of primary undifferentiated cardiac sarcomas found in the archives of the Royal Marsden and Royal Brompton Hospitals, London, UK during the period 2000-2009. Five cases with appropriate consent and archived material were investigated using immunohistochemistry. We found that the spindle, pleomorphic or occasionally epithelioid cell sarcomas showed no lineage-specific differentiation other than partial myofibroblastic or 'myoid' differentiation (all cases). All tumours showed some degree of cytoplasmic positivity for the mesenchymal stem cell marker CD44. In contrast, no nuclear octamer binding protein 3/4 (Oct3/4) expression was seen in any of the tumours, although very patchy cytoplasmic positivity was seen in some tumours. CONCLUSIONS: The cytoplasmic positivity for CD44 and the absence of nuclear Oct3/4 suggest that the cells of these sarcomas may represent 'daughter' stem cells that no longer have the capacity for tumour initiation, but have subsequently developed new lines of partial differentiation. Primary cardiac sarcomas may arise from mesenchymal stem cells with the ability to generate tumours with multilineage differentiation.