Evaluating and Reporting Gastrointestinal Stromal Tumors after Imatinib Mesylate Treatment

Malignant and advanced gastrointestinal stromal tumors (GIST) are currently treated with imatinib mesylate, an inhibitor of KIT and PDGFRA receptor tyrosine kinase. Pathologic evaluation of residual disease is the gold standard in these cases, as clinical and radiologic assessments of treatment response do not always correlate with the pathologic response. Phenotypic and genotypic changes may also occur which may have an impact on treatment decisions. This review will focus on the role of the pathologist in ordering appropriate testing for the primary tumor, the morphologic, phenotypic and genotypic changes seen following imatinib therapy in cases of advanced GIST, and essential components of the pathology reports.