Immunohistochemical testing of GISTs using CD117 markers: the UK NEQAS ICC & ISH external quality assessment data show significant differences in the performance of methods in regular use

Abstract

BACKGROUND CD117 (c-KIT) is a tyrosine kinase receptor protein, mutations in which are important in the tumourigenesis of gastrointestinal stromal tumour (GIST). Immunohistochemical detection of CD117 is the primary identifying diagnostic feature. METHODS UK NEQAS ICC & ISH conducts an EQA programme for CD117 expression in GIST. Between May-2020 and May-2025 20 runs were undertaken. Archived data was analysed to look for evidence regarding testing quality associations with primary antibodies. RESULTS Total submissions were 2,656 (mean per run = 132.8; range = 125-140). Number of submissions awarded a quality score indicating at least acceptable stain quality was 2,642 (99.5%). Total number of submissions that failed was 14 (mean proportion per run = 0.5%; range = 0.0%-2.4%); those obtaining a borderline score totaled 158 (mean proportion = 5.9%; range = 0.7%-10.9%); those obtaining an acceptable score totaled 394 (mean proportion = 14.8%; range = 4.3-24.4%); and those obtaining a good/excellent score totaled 2,090 (mean proportion = 78.7%; range = 57.7%-94.2%). There was a strong trend for the proportion of submissions obtaining a good/excellent score to increase over time. Four primary antibodies were used: Clone 9.7 (102 submissions, 3.9%), YR145 (263 submissions, 10.0%), EP10 supplied by Leica Biosystems (EP10(LB), 415 submissions, 15.8%), EP10 supplied by Roche Diagnostics (EP10(RD), 505 submissions, 19.2%), and a polyclonal antiserum supplied by Agilent Dako (1263 submissions, 48.1%). In addition a total of 76 submissions (2.9%) that used other primaries or suppliers were excluded from the subsequent analyses. CONCLUSIONS Demonstration of CD117 overexpression in GIST was undertaken to a very high quality standard in the majority of laboratories. For users of Dako Agilent supplied automation the highest quality staining was produced by using the polyclonal antiserum from the same supplier. Among users of Leica Biosystems and Roche Diagnostics automation the best staining was produced by using primary sourced from the same supplier that provided their automation. It is recommended that Clone 9.7 (Roche Diagnostics) should not be used as the results it produced were statistically significantly inferior to those of all other antibodies.