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Comment & Response |

Competing Risk of Death in Kaplan-Meier Curves When Analyzing Subsequent Keratinocyte Cancer

Joris A. C. Verkouteren, MD1; Tamar Nijsten, MD, PhD1; Loes M. Hollestein, PhD1,2
[+] Author Affiliations
1Department of Dermatology, Erasmus University Medical Center, Rotterdam, the Netherlands
2Department of Research, Netherlands Comprehensive Cancer Organization, Utrecht, the Netherlands
JAMA Dermatol. 2016;152(4):493-494. doi:10.1001/jamadermatol.2015.5152.
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To the Editor We have read with great interest the article by Wehner et al1 about the timing of subsequent new keratinocyte carcinomas in patients who present with basal cell carcinoma (BCC) or cutaneous squamous cell carcinoma (SCC).1 The authors estimated the probability of developing a subsequent KC by calculating 1 minus the Kaplan-Meier (KM) survival probability. The use of the KM method for other end points than overall mortality can lead to a violation of a key assumption, which is the independent censoring assumption. In a KM curve with subsequent KC as the event of interest, patients who die are censored. The independent censoring assumption means that we assume that patients who are censored at time t have the same risk of developing the event of interest as those patients who are still in follow-up at time t. It is impossible to develop a KC after death, and not adjusting for this will lead to an overestimation of the probability of developing a new KC.

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Kaplan-Meier Curve vs Cumulative Incidence Curve of the Probability of Developing a Second Keratinocyte Cancer (KC)

The solid line represents the biased Kaplan-Meier estimate of the probability of a subsequent KC due to the competing risk of death. The dotted line represents the correct probability of a subsequent KC using a cumulative incidence curve, taking the competing risk of death into account.

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April 1, 2016
Mackenzie R. Wehner, MD, MPhil; Eleni Linos, MD, DrPH; W. John Boscardin, PhD; Mary-Margaret Chren, MD
1Department of Dermatology, University of Pennsylvania, Philadelphia
2Department of Dermatology, University of California, San Francisco
3Department of Epidemiology and Biostatistics, University of California, San Francisco
2Department of Dermatology, University of California, San Francisco4Dermatology Service, San Francisco Veterans Affairs Medical Center, San Francisco, California
JAMA Dermatol. 2016;152(4):494-495. doi:10.1001/jamadermatol.2015.5153.
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