Stem cell markers can aid in determining origin of pediatric sarcomas

Sarcomas are cancerous tumors of the soft tissue and bone. Although they are rare in children, they present a medical challenge when they occur. Diagnosis and treatment of a group of malignancies known as pediatric undifferentiated soft tissue sarcomas are difficult because their cell of origin is unknown. Finding ways to differentiate tumors will lead to better diagnosis and more specific therapies.

The authors of a report in the current issue of the journal Pediatric and Developmental Pathology sought to use stem cell markers as an aid in determining the cell of origin. The expression of stem cell-associated proteins shows differences that can help identify how the tumors evolve. Eighty-one tumors were analyzed, all diagnosed in patients under 18 years old.

Recently, two distinct subtypes of the pediatric undifferentiated soft tissue sarcomas have emerged: those with primitive round cell morphology and those with a more spindled and loose appearance. Two other subcategories have also been identified.

Research has indicated that certain sarcomas come from the mesenchymal stem cells. However, expression of neural stem cells has been noted in others. Identifying and isolating mesenchymal stem cells and neural stem cells relies on finding specific proteins expressed by both types.

In this study, eight different markers representing proteins associated with these two types of stem cells were applied to the 81 tumors. Through cluster analysis, the researchers organized the data into groups showing similar patterns. Two major subgroups of pediatric sarcomas emerged.

Within one of these subgroups, the application of one mesenchymal marker, CD166, showed additional separation between types of tumors. This is significant in that it indicates that undifferentiated soft tissue sarcomas and Ewing sarcoma/primitive neuroectodermal tumors have a common origin. Further research may indicate that some undifferentiated sarcomas belong to the Ewing family of tumors.