Soft Tissue Tumors of Uncertain Origin

Abstract

Many soft tissue tumors of childhood lack obvious differentiation toward a defined mesenchymal tissue type or have a phenotype that does not correspond to any defined normal tissue. These challenging tumors are currently regarded as neoplasms of uncertain differentiation. Nonetheless, there have been great strides in the understanding of their pathologic and genetic features and biologic underpinnings. The application of new genetic information to the pathologic diagnosis among this group of tumors is an emerging area in diagnostic pediatric pathology. This article reviews the clinicopathologic features of tumors of uncertain and/or miscellaneous origin, with an emphasis on the unique aspects of these neoplasms in children and adolescents, use of diagnostic adjuncts, and differential diagnosis.

Soft Tissue Masses

“…Resectable disease has an excellent outcome, with 89 % 5-year survival [ 69 ]. Overall 5-year survival rate is 83 % in children [ 70 ].…”

“…Though it may arise from striated muscle cells, the cell of origin is unclear [ 69 ]. Alveolar soft part sarcoma is somewhat atypical among sarcomas in that it is more common in girls than boys, particularly during childhood.…”

“…It usually arises in the striated muscles of the extremities and rarely in the head and neck [ 92 ]. The tumor may have an indolent course, and there are reports of metastases appearing after decades of complete remission [ 69 ]. Metastases to bone are common, often near the tumor.…”

“…Proximal lesions are more aggressive and have a worse prognosis, with about 60 % disease-specifi c mortality [ 89 ]. Evaluation of gross pathology reveals a lobulated mass with necrosis, hemorrhage, and hyalinized portions [ 69 ]. It is composed of sheets of large atypical epitheliod cells with vesicular nuclei, large nucleoli, and a rhabdoid phenotype.…”

“…Patients who undergo postsurgical radiation have a better prognosis. Young patients whose tumors are small, in the hand, knee or foot, and without metastases have a better prognosis [ 69 ]. The prognosis is worse for boys [ 70 ].…”