Pathologic evaluation of pediatric soft tissue tumors.

The subject of soft tissue tumors in children has some parallels with the same topic in adults, but many of the details clearly establish the existence of distinct differences. Most soft tissue tumors in adults arise in the extremities or in the superficial and deep soft tissues elsewhere in the body, and most tumors are neoplastic, whether they are benign or malignant. In children, some of the most common soft tissue tumors may not be neoplastic at all, but rather are malformations of the supporting mesenchymal tissues. There is a common classification of soft tissue tumors that is applicable to both pediatric- and adult-type neoplasms. Although some of the "adult"-type soft tissue tumors may occur in children, the reverse situation is very uncommon. Because pediatric soft tissue tumors are not seen with any regularity by many pathologists in a practice dominated by adult cases, there is less familiarity and more uncertainty about these tumors in children. The differential diagnosis of a malignant soft tissue tumor in a child encompasses the broad morphologic spectrum of spindle cells, round cells, or combined-pattern neoplasms. The diagnostic process is complex and may necessitate an array of ancillary studies, including immunohistochemistry, electron microscopy, and molecular diagnostics. After a decision is reached to excise a soft tissue sarcoma in a child, many of the steps in the examination of the specimen and the reporting of results for diagnostic and staging purposes are similar to those in the evaluation of a soft tissue sarcoma in an adult. However, it is important for the pathologist and other members of the multidisciplinary health care team to remember that a soft tissue tumor in a child may have genetic implications that directly influence the care of the patient and the family and for which the excised tissue offers a potentially invaluable resource for future studies.