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Arch Pathol Lab Med. 2013 Nov;137(11):1545-9. doi: 10.5858/arpa.2012-0561-CP.

A prospective, multi-institutional diagnostic trial to determine pathologist accuracy in estimation of percentage of malignant cells.

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  • 1From the Department of Pathology, Yale University School of Medicine, New Haven, Connecticut (Dr Viray, Mr Li, Dr Rimm); the Biostatistics (Mr Long) and Surveys (Ms Vasalos) Departments, College of American Pathologists, Northfield, Illinois; the Department of Pathology & Microbiology, University of Nebraska Medical Center, Omaha (Dr Bridge); the Department of Pathology & Laboratory Medicine, Northwestern University Feinberg School of Medicine, Chicago, Illinois (Dr Jennings); the Department of Pathology, Mayo Clinic, Rochester, Minnesota (Dr Halling); and the Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, New York (Dr Hameed).



The fraction of malignant cells in tumor tissue submitted for tests of genetic alterations is a critical variable in testing accuracy. That fraction is currently determined by pathologist visual estimation of the percentage of malignant cells. Inaccuracy could lead to a false-negative test result.


To describe a prospective, multi-institutional study to determine pathologist estimation accuracy.


Ten ×20 magnification images of hematoxylin-eosin-stained colon tissue specimens were sent as an educational component of the College of American Pathologists KRAS-B 2011 Survey. Data from 194 labs were analyzed and compared to a criterion standard with comprehensive manual nuclear counts.


Survey responses indicated low interlaboratory precision of pathologist estimation, but mean estimates were fairly accurate. A total of 5 of the 10 cases assessed showed more than 10% of respondents overestimating in a manner that could lead to false-negative test results.


The significance of estimation errors resulting in molecular testing failures with implications for patient care is unknown, but the current study suggests false-negative test results may occur.

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