Funding for this research was provided by:
Received: 26 February 2020
Accepted: 19 May 2020
First Online: 30 May 2020
Ethics approval and consent to participate
: Data were linked after applying and obtaining administrative permissions from the Cancer Registry of Norway (reference number: 17/241 DU-3018), the Norwegian Patient Registry (reference number: 17/13875–11) and Statistics Norway (reference number: 17/1514). The Norwegian Regional Ethics Committee concluded that no approval was needed for this study and waived the need for informed patient consent (reference number: 2017/428REK sør-øst A). Thus, they gave the authors exemption from the statutory duty of confidentiality. The approval of handling indirect identifiable data was obtained from the Data Protection Officer (PVO) (reference number: 2017/6597).
: Not applicable.
: The authors declare that they have no competing interests.