Background: Mesenchymal chondrosarcoma (MCS) is a distinct, very rare sarcoma with little evidence supporting treatment recommendations. Patients and methods: Specialist centres collaborated to report prognostic factors and outcome for 113 patients. Results: Median age was 30 years (range: 11-80), male/female ratio 1.1. Primary sites were extremities (40%), trunk (47%) and head and neck (13%), 41 arising primarily in soft tissue. Seventeen patients had metastases at diagnosis. Mean follow-up was 14.9 years (range: 1-34), median overall survival (OS) 17 years (95% confidence interval (CI): 10.3-28.6). Ninety-five of 96 patients with localised disease underwent surgery, 54 additionally received combination chemotherapy. Sixty-five of 95 patients are alive and 45 progression-free (5 local recurrence, 34 distant metastases, 11 combined). Median progression-free survival (PFS) and OS were 7 (95% CI: 3.03-10.96) and 20 (95% CI: 12.63-27.36) years respectively. Chemotherapy administration in patients with localised disease was associated with reduced risk of recurrence (P = 0.046; hazard ratio (HR) = 0.482 95% CI: 0.213-0.996) and death (P = 0.004; HR = 0.445 95% CI: 0.256-0.774). Clear resection margins predicted less frequent local recurrence (2% versus 27%; P = 0.002). Primary site and origin did not influence survival. The absence of metastases at diagnosis was associated with a significantly better outcome (P < 0.0001). Data on radiotherapy indications, dose and fractionation were insufficiently complete, to allow comment of its impact on outcomes. Median OS for patients with metastases at presentation was 3 years (95% CI: 0-4.25). Conclusions: Prognosis in MCS varies considerably. Metastatic disease at diagnosis has the strongest impact on survival. Complete resection and adjuvant chemotherapy should be considered as standard of care for localised disease.

Background: Knowledge of chondrosarcoma (CS) of bone to date is based on institutional reports and registry publications with limits in reporting, detail and quality of data. Method: We have performed a retrospective search of CS of bone in the National Cancer Registry in Norway from 1990-2013, cross checked against local tumor databases with further quality control and supplementation of all data from clinical files. The time period is defined by the routine use of axial imaging in clinical practice. A total of 311 cases are included. We performed 108 pathological reviews and 223 radiological reviews. The manuscript was prepared according to the STROBE checklist for strengthening of observational studies. We performed uni-/multivariate cox analyses to define independent prognostic variables from the main cohort of central CS of bone. Results: The incidence of CS of bone in Norway is 2.85/million/yr. for both sexes overall, rising to 3.45/million/yr. in the last 5-year period. There is an increase in the most common central CS subtype, stronger for women than for men. Central CS had, in general 10-15% local recurrence rates, all evident by 5 years while metastasis rate increases with location and grade. Exceptions are extremity grade 1 CS which displayed no metastatic events and axial grade-3 disease with high rates (50%) of both local and metastatic relapse. Peripheral CS had limited metastatic potential (2%), but rates of local relapse (13%) continue to appear towards 10 years of follow up. Malignancy grade 3 independently predicts rate of metastasis and presence of soft tissue component predicts local recurrence, metastasis and survival. Conclusion: Rates of local recurrence, metastasis and disease specific survival follow clear patterns depending on subtype, location and grade allowing better tailoring of follow-up regimes. Malignancy grade 3 and the presence of a soft tissue component independently predict behavior for central CS of bone. ARTICLE HISTORY

Background and Objectives: Interobserver variability in histological grading of central conventional chondrosarcoma (CCCS) limits the quality of patient information and research progression. We aim to quantify known and new prognostic variables and propose a risk stratification model. Method: We selected 149 cases from the Cancer Registry of Norway. Cox proportional hazard models were estimated. Based on these results a dichotomous risk classification was proposed and presented by Kaplan-Meier estimates for rates of local recurrence, metastasis, and disease-specific survival. Results: The influence of axial skeletal location (Hazard ratio [HR] = 19.06), a soft tissue component ≥1 cm (HR = 13.45), and histological grade 3 (HR = 16.46) are all significant in predicting the rate of metastasis. The creation of a variable combining axial skeletal location and a soft tissue component ≥1 cm strongly predicts the risk of metastasis (HR = 14.02; P < .001) and death (HR = 2.74; P = .030) at multivariate analysis, making the histological grade insignificant. Together with metastasis at diagnosis (HR = 285.65; P < .001), this forms the basis of our proposed risk stratification, producing a small highrisk group (39 cases with 33% risk of metastasis) and a large low-risk group (103 cases with 2% risk of metastasis) without a histological grade. Conclusion: Axial skeletal location and a soft tissue component ≥1 cm combined divides a CCCS cohort into low-and high-risk groups without a histological grade.