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

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 ×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. 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 sig...