Antigen retrieval and primary antibody type affect sensitivity but not specificity of CD117 immunohistochemistry

Aims:  To investigate the effects of antigen retrieval and primary antibody selection on specificity and sensitivity of CD117 immunohistochemistry.
Methods and results:  A survey and literature review were performed to determine the most commonly used CD117 antibodies. Of six such antibodies, three (Neomarkers polyclonal RB-1518, Novocastra monoclonal T595 and Santa Cruz polyclonal C19) were rejected as only suboptimal immunoreactivity was produced despite the use of various immunohistochemical protocols. Immunohistochemistry using the three remaining antibodies (Cell Marque polyclonal CMC766, Dako polyclonal A4502 and Epitomics monoclonal YR145) was performed, with and without (for Dako and Epitomics antibodies) antigen retrieval, on 32 gastrointestinal stromal tumours (GISTs) and on 139 neoplasms (comprising 24 neoplasm types) that are differential diagnoses for GIST and/or have been reported to express CD117. Antigen retrieval generally increased the sensitivity but did not alter the specificity of immunoreactivity with the three antibodies. The different antibodies showed variations in sensitivity, but did not stain different spectrums of neoplasm type. A small number of neoplasms showed scattered nuclear immunopositivity (particularly seen without antigen retrieval), which was regarded as representing cross-reactivity.
Conclusions:  Antigen retrieval and changing between the three antibodies tested affect sensitivity but not specificity of CD117 immunohistochemistry. Antigen retrieval does not produce false-positive CD117 immunostaining.