Public Defence: Joachim Thorkildsen Joachim Thorkildsen at Institute of Clinical Medicine will be defending the thesis "Chondrosarcoma in Norway 1990-2013; Risk stratification without histology" for the degree of Philosophiae Doctor (PhD).

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Photo: Per Marius Didriksen, OUS HF

An electronic copy of the thesis may be ordered from the faculty up to 2 days prior to the public defence. Inquiries regarding the thesis after the public defence must be addressed to the candidate.

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Adjudication committee

  • First opponent: Professor Lee Jeys, The Royal Orthopaedic Hospital, Birmingham, United Kingdom
  • Second opponent: Senior Consultant Mikael Skorpil, Karolinska University Hospital, Stockholm, Sweden
  • Third member and chair of the evaluation committee: Professor II Kjersti Flatmark, Institute of Clinical Medicine, University of Oslo

Chair of defence

Associate Professor Thomas Johan Kibsgård, Institute of Clinical Medicine, University of Oslo

Principal Supervisor

Orthopaedic surgeon, PhD Olga Zaikova, Oslo University Hospital, The Norwegian Radium Hospital


We have developed a simple method of risk stratification for a rare cancer; Chondrosarcoma of bone. This is not reliant on the use of microscopic histological assessment (grade) which has been the primary tool for risk assessment during the last 50 years. This allows identification of a small group with high risk and a large group with low risk.

We used the Cancer Registry of Norway to identify patients with chondrosarcoma from 1990-2013 and quality controlled all data for 311 patients. The incidence was 2.85 per million per year overall. There was an increase in incidence over the study period, due to an increase in the most common central subtype. Each subtype of chondrosarcoma has its unique pattern and frequency of relapse over time, allowing significant tailoring and shortening of follow-up, compared to earlier recommendations.

In some cases of the central subtype, the tumour breaks through the bone, growing into the surrounding tissue (soft tissue component). This was associated with an increased risk of local and systemic relapse as well as death. Skeletal location (extremity vs axial) and the size of the soft tissue component are also important markers of prognosis. For those in whom the tumour is located in the axial skeleton combined with a soft tissue component ≥1cm (39 patients), the rate of metastasis was 33%- “Oslo highrisk”. The rest comprises 103 patients with 2% rate of metastasis- “Oslo lowrisk”. By this distinction, the majority of patients had a low risk of adverse disease course.

Half of local recurrence from central chondrosarcoma were discovered due to symptoms from the patients. The other half by imaging at routine follow-up. Dedifferentiation and upgrading were seldom events. Local recurrence was associated with risk of metastasis and death overall, but not for all cases. Those with aggressive disease at primary diagnosis also had aggressive disease at recurrence. Oslo risk from the primary setting also appeared to predict risk at recurrence.

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Published Oct. 29, 2021 11:15 AM - Last modified Nov. 16, 2021 1:15 PM