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Statistical Methods for Colorectal Neoplastic Prevention Trials

Colorectal cancer is one of the most common malignancies in the United States. There is an increasing number of studies using recurrent colorectal adenomas to evaluate the prevention effect for some promising agents. The number of recurrent colorectal adenomas is often measured by performing colonoscopy, which is known to miss a small percentage of existing adenomas and result in misclassification on recurrence status. In addition, some participants might not comply with the schedule of follow-up colonoscopy, which is scheduled to be performed once at the end of the study and, therefore, have variable follow-up lengths compared to the compliant participants. The reasons that a participant cannot comply with the schedule of follow-up colonoscopy could be informative of the risk of recurrence and then bias the results derived from statistical methods that do not adjust for noncompliance. Conventional statistical methods for colorectal adenoma prevention trials cannot simultaneously incorporate misclassification and variable follow-up into analysis and cannot adjust for informative non-compliance without strong assumptions and, furthermore, may incorrectly produce equivocal results for some promising nutritional or chemopreventive agents. The purpose of this application was to develop sophisticated and appropriate statistical models to describe the relationship between the preventive agents and recurrence of colorectal adenomas. We used a latent variable recurrence model, which assumed a portion of non-recurrent participants were misclassified due missing existing adenomas at follow-up colonoscopy, to handle misclassification and a weight function to incorporate the length of follow-up into analysis. The prognostic factors for risk of recurrence was incorporated into the weight function to adjust for potential informative non-compliance. The hope was that a  better understanding of the relationship between preventive agents and recurrence of colorectal adenomas would allow clinical investigators to identify an agent that truly reduces recurrence of colorectal adenomas. This project was funded through a grant from the National Cancer Institute. 

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