BackgroundCancer registries collect patient-specific information about cancer diseases. The collected information is verified and made available to clinical researchers, physicians, and patients. When processing information, cancer registries verify that the patient-specific records they collect are plausible. This means that the collected information about a particular patient makes medical sense.MethodsUnsupervised machine learning approaches can detect implausible electronic health records without human guidance. Therefore, this article investigates two unsupervised anomaly detection approaches, a pattern-based approach (FindFPOF) and a compression-based approach (autoencoder), to identify implausible electronic health records in cancer registries. Unlike most existing work that analyzes synthetic anomalies, we compare the performance of both approaches and a baseline (random selection of records) on a real-world dataset. The dataset contains 21,104 electronic health records of patients with breast, colorectal, and prostate tumors. Each record consists of 16 categorical variables describing the disease, the patient, and the diagnostic procedure. The samples identified by FindFPOF, the autoencoder, and a random selection—a total of 785 different records—are evaluated in a real-world scenario by medical domain experts.ResultsBoth anomaly detection methods are good at detecting implausible electronic health records. First, domain experts identified\documentclass[12pt]{minimal}
				\usepackage{amsmath}
				\usepackage{wasysym} 
				\usepackage{amsfonts} 
				\usepackage{amssymb} 
				\usepackage{amsbsy}
				\usepackage{mathrsfs}
				\usepackage{upgreek}
				\setlength{\oddsidemargin}{-69pt}
				\begin{document}$$8\%$$\end{document}8%of 300 randomly selected records as implausible. With FindFPOF and the autoencoder,\documentclass[12pt]{minimal}
				\usepackage{amsmath}
				\usepackage{wasysym} 
				\usepackage{amsfonts} 
				\usepackage{amssymb} 
				\usepackage{amsbsy}
				\usepackage{mathrsfs}
				\usepackage{upgreek}
				\setlength{\oddsidemargin}{-69pt}
				\begin{document}$$28\%$$\end{document}28%of the proposed 300 records in each sample were implausible. This corresponds to a precision of\documentclass[12pt]{minimal}
				\usepackage{amsmath}
				\usepackage{wasysym} 
				\usepackage{amsfonts} 
				\usepackage{amssymb} 
				\usepackage{amsbsy}
				\usepackage{mathrsfs}
				\usepackage{upgreek}
				\setlength{\oddsidemargin}{-69pt}
				\begin{document}$$28\%$$\end{document}28%for FindFPOF and the autoencoder. Second, for 300 randomly selected records that were labeled by domain experts, the sensitivity of the autoencoder was\documentclass[12pt]{minimal}
				\usepackage{amsmath}
				\usepackage{wasysym} 
				\usepackage{amsfonts} 
				\usepackage{amssymb} 
				\usepackage{amsbsy}
				\usepackage{mathrsfs}
				\usepackage{upgreek}
				\setlength{\oddsidemargin}{-69pt}
				\begin{document}$$22\%$$\end{document}22%and the sensitivity of FindFPOF was\documentclass[12pt]{minimal}
				\usepackage{amsmath}
				\usepackage{wasysym} 
				\usepackage{amsfonts} 
				\usepackage{amssymb} 
				\usepackage{amsbsy}
				\usepackage{mathrsfs}
				\usepackage{upgreek}
				\setlength{\oddsidemargin}{-69pt}
				\begin{document}$$26\%$$\end{document}26%. Both anomaly detection methods had a specificity of\documentclass[12pt]{minimal}
				\usepackage{amsmath}
				\usepackage{wasysym} 
				\usepackage{amsfonts} 
				\usepackage{amssymb} 
				\usepackage{amsbsy}
				\usepackage{mathrsfs}
				\usepackage{upgreek}
				\setlength{\oddsidemargin}{-69pt}
				\begin{document}$$94\%$$\end{document}94%. Third, FindFPOF and the autoencoder suggested samples with a different distribution of values than the overall dataset. For example, both anomaly detection methods suggested a higher proportion of colorectal records, the tumor localization with the highest percentage of implausible records in a randomly selected sample.ConclusionsUnsupervised anomaly detection can significantly reduce the manual effort of domain experts to find implausible electronic health records in cancer registries. In our experiments, the manual effort was reduced by a factor of approximately 3.5 compared to evaluating a random sample.