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

Viray, H.; Li, K.; Long, T. A.; Vasalos, P.; Bridge, J. A.; Jennings, L. J.; Halling, K. C.; Hameed, M.; Rimm, D. L.

Arch Pathol Lab Med. 2013 Oct 31; 137(11):1545-9


Context.-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. Objective.-To describe a prospective, multi-institutional study to determine pathologist estimation accuracy. Design.-Ten x20 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. Results.-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. Conclusions.-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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