[Skip to Navigation]
Comment & Response
April 2018

Lower Cancer Incidence—Warfarin Effect or Immortal Time Bias?

Author Affiliations
  • 1Hospital Pharmacy of Tromsø, Tromsø, Norway
  • 2Norwegian Institute of Public Health, Oslo, Norway
  • 3Department of Pharmacy, UiT - The Arctic University of Norway, Tromsø, Norway
JAMA Intern Med. 2018;178(4):585. doi:10.1001/jamainternmed.2018.0370

To the Editor In an Original Investigation by Haaland and colleagues1 recently published in an issue of JAMA Internal Medicine, the authors reported that use of warfarin is associated with lower incidence of cancer. We believe this study is subject to several methodological flaws that undermine its validity.

First, the authors1 did not adjust for any confounders but sex and age. Norway has several nationwide registries that could have provided information on potential confounders including comorbidities and medical treatment. Furthermore, they did not exclude or adjust for previous cancer before 2006, even though the Cancer Registry has collected data since 1951. The claim that incident cancer was studied is misleading. The lack of confounder adjustment is not properly addressed, and the reader is left to speculate on the magnitude and direction of these issues.

Add or change institution
Limit 200 characters
Limit 25 characters
Conflicts of Interest Disclosure

Identify all potential conflicts of interest that might be relevant to your comment.

Conflicts of interest comprise financial interests, activities, and relationships within the past 3 years including but not limited to employment, affiliation, grants or funding, consultancies, honoraria or payment, speaker's bureaus, stock ownership or options, expert testimony, royalties, donation of medical equipment, or patents planned, pending, or issued.

Err on the side of full disclosure.

If you have no conflicts of interest, check "No potential conflicts of interest" in the box below. The information will be posted with your response.

Not all submitted comments are published. Please see our commenting policy for details.

Limit 140 characters
Limit 3600 characters or approximately 600 words