Soft tissue sarcomas (STS) are rare tumors accounting for less than 1% of all cancers, corresponding to approximately 200 new cases in Denmark annually.

They comprise a heterogenic group of malignancies arising from the embryonic mesoderm. They are classified according to their presumed tissue of origin, or their morphological appearance, into more than 50 histological subtypes, with pleomorphic sarcoma, liposarcoma, and leiomyosarcoma being the most common STSs.

STS can occur at any age, but is most commonly seen, except for a few histological subtypes, in middle-aged adults. Although they can arise in any anatomical location or organ in the body, the majority occurs in the muscle groups of the extremities and trunk wall.

Most sarcoma arise de novo without identifiable etiology, even though previous irradiation and predisposing genetic mutations have been shown to be associated with certain histological subtypes.

The treatment of STS in the extremity and trunk wall consists primarily of surgical excision with a margin of surrounding tissue. This is usually combined with different regimes of radiotherapy, administered either pre- or postoperatively, according to grade, margin, and local preferences. The use of adjuvant chemotherapy as part of the standard treatment is, except for certain histological subtypes, still controversial. While meta-analyses have suggested increased survival in patients at high risk, this has not been confirmed in randomized controlled trials.

Even though the diagnostic tools, treatment possibilities, etc. have changed significantly during the decades, no apparent change in the prognosis for patients with non-metastatic STS has been seen. Approximately 20% develop local recurrence, while 30% develop distant metastasis, most frequently to the lungs. The majority of patients with metastatic disease will die of their STS. Thus, in order to identify patients who might benefit from more intensive treatment studies of prognostic factors are crucial.

Studies are often complicated by the rarity of STS, rendering it difficult to conduct high evidence research such as randomized controlled trials. Thus the majority of studies are based on retrospectively collected data from major tertiary sarcoma units. These data are often compiled into clinical databases, which ensure large sample sizes, long follow-up periods, and high external validity. However, when clinical databases are used, validation of data is either not reported or not done, although it is a crucial factor in determining the quality and value of the results reported.