Prognostic information in soft tissue sarcoma using tumour size, vascular invasion and microscopic tumour necrosis—the SIN-system

We have earlier devised a system for soft tissue sarcoma (STS), based on three negative prognostic features: large tumour size, vascular invasion, and microscopic tumour necrosis, the SIN-system. Tumours which exhibit 2 or 3 of these features are categorised as high-risk, the others as low-risk. We have now tested this system for reproducibility both as regards recognition of its components, and as regards prognostic strength in patients from another institution. We have also compared it with the American Joint Committee on Cancer (AJCC) system. 200 patients with STS were analysed, all had been treated by surgery, in 97 patients combined with radiotherapy. The median follow-up for the 117 survivors was 10 (1.5-27) years. Without knowledge of the clinical data, three groups of pathologists independently reviewed original slides from all of the tumours. Based on the factors, the tumours were classified as high-risk or low-risk. The prognostic strength was compared using the results obtained by the different observers. Concordance in recognition of vascular invasion, tumour necrosis, and overall grading was seen in 156 (78%), 154 (77%), and 167 (84%) of the 200 tumours, respectively. Based on the different observers' grading, the cumulative 5-year metastasis-free survival rate (MFSR) varied for patients with low-risk tumours between 0.85 and 0.80, and for patients with high-risk tumours between 0.48 and 0.43. The Kappa-value for grading between all three groups of observers was 0.77. The SIN-system gave more clinically useful prognostic information than the AJCC system. Useful prognostic information in STS can be obtained by using tumour size, vascular invasion and microscopic tumour necrosis. This system provides two distinct prognostic groups, and has a high reproducibility.