Sarcomas are malignant tumors formed by cells derived from mesenchymal stem cells. Mesenchymal stem cells give rise to a variety of cell types, and sarcomas can be classified based off the type of tissue making up the tumor. NRSTS are sarcomas whose tissue presents without features of either bone or skeletal muscle tissue:
Non-rhabdomyosarcoma soft tissue sarcoma: not skeletal muscle tissue
Since mesenchymal stem cells can differentiate into a large variety of cells, and since NRSTS encompass all sarcomas composed of neither bone nor skeletal muscle tissue, there are a large variety of NRSTS. There are over 50 histological subtypes of NRSTS.[2] Below are examples of NRSTS presented within the 2020 WHO Classification of Tumors of Soft Tissue.[3][2]
NRSTS most commonly present as a painless, enlarging mass in the trunk or extremities.[1] Symptoms depend on the location of the tumor and its effect on nearby structures, potentially causing numbness, weakness, pain, swelling or organ dysfunction.[1] If the NRSTS spreads then it can cause systemic symptoms.[1]
Diagnosis
The rarity and diversity of NRSTS impedes their diagnosis.[2] Diagnosis requires a biopsy of the tumor to characterize the tumor cells and their molecular features (genetics, epigenetics, proteome, etc.).[2] Radiological imaging (MRIs, X-rays, CT scans, etc.) can help locate or determine the extent of the NRSTS.[2]
Treatment
Surgery is the primary treatment for the majority of NRSTS, usually being the only treatment for resected (surgically removed), low-grade tumors.[1] In other cases, radiation therapy with or without chemotherapy are considered.[1] The majority of unresectable, localized NRSTS, become resectable following treatment with chemotherapy and/or radiation therapy.[1]
Chemotherapy can be used on large, high-grade tumors to help prevent them from metastasizing—spreading throughout the body.[1] If the NRSTS has spread then chemotherapy can also be used to aid with system-wide control of the cancer.[1] Due to their diversity, NRSTS have more variable and unpredictable responsiveness to chemotherapy than rhabdomyosarcomas.[1]
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