Intratumor DNA heterogeneity—as assessed by flow-cytometric cellular DNA analysis—is predictive of prognosis in many types of cancer. But some truly heterogeneous tumors apparently have a substantial chance of being misclassified as normal. One way to enhance the assay's sensitivity is to test multiple samples from each tumor specimen. This article describes an analysis of data from a study of endometrial cancer, with a view to establishing the number of samples needed to test to reliably assess heterogeneity. The analysis involves selection of a model for the data and estimation of test sensitivity and predictive value. We analyze the data from both Bayesian and frequentist perspectives. The data suggest that the degree of within-tumor correlation is relatively high; consequently, there is little to be gained from taking multiple samples per tumor.