Myxofibrosarcoma (MFS) is one of the most common sarcoma subtype in elderly patients. They are reported to recur locally independently of the tumour grade in 30-40% of cases and metastases are reported to develop in high-grade tumours in 20-35% cases. As MFS is a rare diagnosis, data investigating specific survival and independent risk factors are lacking and have mostly been limited to single orthopaedic oncology centre studies so far. Thus we set up a pathology-based retrospective study and analyzed all MFS diagnosed in our institution with the following aims: (1) analysis of independent risk factors for overall survival, disease specific survival, local recurrence-free survival and distant metastasis free survival following resection of MFS; (2) analysis of resection margin status.

High-grade MFS have a low survival distant metastasis free survival and local recurrence free survival is dependent on surgical margin status.

We retrospectively analysed 109 patients (median 66 years [range, 21–96]) diagnosed with MFS and a median follow-up of 42 months at one centre between 1990 and 2014. Tumor-associated survival, including competing risk analysis, and prognostic factors for local recurrence, metastatic disease and death from disease were investigated and included in a multivariate analysis.

Overall survival was 79% [95%CI: 71.9–87.5] at 3 years and 76% [95%CI: 67.4–84.6] at 5 years. Disease specific survival was 85% [95%CI: 78.4–92.2] at 3 years and 80% [95%CI: 72.2–88.2] at 5 years. There were local recurrences in 11/109 patients (10%). Local recurrence free survival (LRFS) was 95% [95%CI: 92.0–99.8] at 3 and 88% [95%CI: 84.3–96.4] at 5 years. Metastatic disease (n=25; 23%) occurred after a median follow-up of 10 months. Distant metastasis free survival was 78% [95%CI: 69.9–85.9] at 3 and 77% [95%CI: 68.4–84.8] at 5 years. R1 status at primary resection was an independent risk factor for decreased Local Recurrence-free survival (OR: 8.5, 95%CI: 1.59–49.79 [p=0.01]). Grading was an independent risk factor for decreased Disease specific survival (OR 13.4, 95%CI: 1.65–1734.84 [p=0.01]) and Distant metastasis free survival (OR 16.2, 95%CI: 2.0–2110.5 [p=0.004]). Primary resection achieved R0 margins in 63 (58%) of 109 patients. Margins were adequate significantly more often (p<0.001) in patients treated primarily at a sarcoma centre (R0=58/68, 85%) than in those treated primarily at non-sarcoma centres (R0= 5/41, 12%), whereby the latter significantly more often treated superficial tumours (p=0.001) with a size of less than 5cm (p<0.001).

Patients with high-grade MFS had a poorer prognosis with respect to Disease specific survival/Distant metastasis free survival than low-grade MFS. Local recurrence did not significantly affect disease specific survival.

IV.