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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.
Verkouteren JAC, Nijsten T, Hollestein LM. Competing Risk of Death in Kaplan-Meier Curves When Analyzing Subsequent Keratinocyte Cancer. JAMA Dermatol. 2016;152(4):493-494. doi:10.1001/jamadermatol.2015.5152