Background: Small (≤ 5 cm) soft tissue sarcomas (STS) of the extremities and the trunk wall generally have a favorable prognosis. However, 1 of 10 patients do develop metastases, and we therefore aimed to determine predictors of metastasis in a population-based cohort of patients with small STSs.
Patients and methods: In the southern Sweden health care region, 848 adult patients with STS of the extremities or the trunk wall were diagnosed between 1986 and 2010. Of these, 243 STS (29 %) were ≤5 cm. Prognostic evaluation was performed in 229 patients with localized disease at diagnosis, 181 of whom had histologic high-grade tumors.
Results: None of the 48 patients with low-grade tumors developed metastases, whereas 24 of 181 patients with high-grade tumors (13 %) tumors did. Presence of either tumor necrosis or vascular invasion predicted development of metastases with a hazard ratio of 2.9 (95 % CI, 1.0-7.9), and tumors with both factors had a hazard ratio of 12 (95 % CI, 4.1-37) for metastasis (adjusted for size).
Conclusions: Our population-based series of STSs ≤5 cm demonstrate an overall good prognosis with metastases developing in 13 % of the patients with high-grade tumors. Tumor necrosis and vascular invasion were the major predictors of metastatic disease in this subset. Tumors with both these risk factors metastasized in 8 of 18 patients, which corresponds to a 12-fold increased risk of metastasis. These findings suggest that although small STS generally are linked to a good prognosis, necrosis and vascular invasion are features indicating biologically aggressive tumors for which treatment and surveillance should equal that for larger tumors.