JSM 2004 - Toronto

Abstract #300958

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Activity Number: 148
Type: Topic Contributed
Date/Time: Monday, August 9, 2004 : 2:00 PM to 3:50 PM
Sponsor: Biometrics Section
Abstract - #300958
Title: Weighted Kaplan-Meier Statistics in the Case of Nonproportional Hazards: An Application in Cancer Prevention
Author(s): Paul H. Frankel*+ and Mary E. Reid and James R. Marshall
Companies: City of Hope National Medical Center and Roswell Park Cancer Institute and Roswell Park Cancer Institute
Address: 1500 East Duarte Rd., Duarte, CA, 91010,
Keywords: survival ; proportional hazards ; Kaplan-Meier ; prevention ; competing risks ; Cox
Abstract:

When comparing tumor progression or patient survival between two arms of a randomized study, proportional hazards always holds under the null hypothesis of no differences in treatment effect. However, if there is a difference between the two arms, the proportional hazard assumption is problematic, particularly in cancer therapeutic and prevention trials. As a result, the power of the log-rank test can be suboptimal and may actually decrease with increasing follow-up time. In therapeutic clinical trials for active disease, accelerated failure or mixed models with a cured fraction can often remedy this problem. In prevention trials, a different approach is required due to the increased magnitude of competing risks. A weighted Kaplan-Meier statistic will be presented as a viable alternative. Based on inverse variance-weighting and an empirical distribution, this method is useful in analyzing survival that does not follow proportional hazards and is not amenable to parametric methods. Data from the Nutritional Prevention of Cancer trial that tested a selenized yeast intervention on cancer prevention, will be used to demonstrate the utility of this test.

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