Doctoral Defense in Medicine – Arnar Snær Ágústsson

On Friday, October 3, 2025, Arnar Snær Ágústsson will defend his doctoral thesis in Medicine at the Faculty of Medicine, University of Iceland.

The thesis is entitled:
Impact of anticoagulation and immunosuppressive drugs on the prognosis of patients with colorectal cancer: a population-based study
(Áhrif blóðþynningar- og bólgueyðandi lyfja á horfur einstaklinga með ristil- og endaþarmskrabbamein: lýðgrunduð rannsókn)

Opponents:
Dr. Martti Farkkila, Professor Emeritus, University of Helsinki
Dr. Richard Goldberg, Professor, West Virginia University School of Medicine, USA

Supervisor:
Professor Einar Stefán Björnsson

Co-supervisor:
Jóhann Páll Hreinsson, Specialist

Doctoral committee members:
Ásgerður Sverrisdóttir, Specialist
Helgi Birgisson, Specialist
Sigrún Helga Lund, Professor
Sigurdís Haraldsdóttir, Professor

The defense will be chaired by Professor Sædís Sævarsdóttir, Dean of the Faculty of Medicine. The ceremony will take place in the Ceremonial Hall (Hátíðasalur) of the University of Iceland and will begin at 9:00 AM.

Abstract

The incidence of Colorectal Cancer (CRC) is increasing, and it‘s one of the leading causes of death due to cancer. The most common presenting symptoms of CRC are gastrointestinal bleeding events, and oral anticoagulants have been shown to increase the risk of such events. However, there are no studies examining whether oral anticoagulants (OACs) could improve survival through potential early detection. Aspirin has been demonstrated to have protective effects against CRC, but its impact on cancer-specific survival has been conflicting. Aspirin‘s effects are believed to be mediated through anti-inflammation. Corticosteroids have multiple and complex effects on inflammation and the immune system, but their potential effects on CRC have not been previously explored.

All four studies were nationwide studies based on retrospective cohort databases. Study I used data from the OAC prescriptions database to examine gastrointestinal bleeding events in OAC users from 2014 to 2019. Studies II, III, and IV were based on the Colorectal Cancer Database from 2000 to 2019 and compared the association of pre-diagnostic medications with CRC outcomes.

Study I demonstrated that OACs increased the risk of bleeding events due to either colonic adenoma or CRC. Anticoagulation use was associated with improved CRC-specific survival, while overall survival was decreased in OAC users. Both of these results further suggest that anticoagulation could potentially lead to early CRC detection with improved CRC-survival. Aspirin users had improved CRC-specific survival, mediated mainly by fewer patients with stage IV disease. This could mean that aspirin could delay or hinder the metastatic development of CRCs. Corticosteroid use prior to CRC diagnosis was associated with worse disease-free survival, with the decreased survival mostly seen 5 years after cancer diagnosis. This could imply that corticosteroids might have negative effects on long-term cancer survival; however, further studies are required to substantiate these findings.

About the doctoral candidate

Arnar Snær Ágústsson was born in 1993 in Akranes and raised in Vík í Mýrdal. He graduated from the Natural Sciences track at Menntaskólinn að Laugarvatni and completed his medical degree in 2020. Following his internship year, he began his residency in Anesthesiology and Intensive Care at Landspítali – The National University Hospital of Iceland, where he works alongside his doctoral studies. During his internship year, Arnar also began his PhD studies at the University of Iceland and received a grant from the Eimskip University Fund.
His parents are Ágúst Freyr Bjartmarsson and Kristín Svafarsdóttir.