Novel perspectives in treatment and follow-up of sarcomas, with a focus on gastrointestinal stromal tumors

Sarcomas are rare and account for only 1% of all adult cancer types. There are more than 50 histologic subtypes of soft tissue sarcomas (STS), which are all subsumed in the World Health Organization (WHO) classification of Tumors of Soft Tissue and Bone. Within the STS group, both gastrointestinal stromal tumors (GIST) and undifferentiated pleomorphic soft tissue sarcomas (UPS) contribute to the most common subtypes of this rare cancer type. This thesis aims to give an insight in new treatments and less invasive follow-up strategies in these common STS subtypes. The first part of this thesis focusses on different aspects of systemic and surgical treatment in patients with GIST, with an emphasis on identifying optimal follow-up strategies by highlighting the use of circulating tumor DNA (ctDNA) as promising follow-up tool. The second part of this thesis concentrates on treatment with radiotherapy in surgically treated older patients with UPS of the extremities.