DOG1 (Clone K9) is Seldom Expressed and Not Useful in the Evaluation of Pancreatic Neoplasms

DOG1, a transmembrane calcium-regulated chloride channel protein, is a sensitive and specific marker for gastrointestinal stromal tumors compared with other spindle cell and epithelioid neoplasms. Overexpression has also been described in a variety of both benign and malignant epithelial neoplasms. Recently, DOG1 immunoreactivity has been reported in pancreatic solid pseudopapillary tumors (SPT), suggesting a role as a marker for SPT. Utilizing immunohistochemistry, we evaluated DOG1 expression in pancreatic neoplasms to determine the prevalence of staining and establish diagnostic utility. Multiple tissue microarrays (TMA) were created from cores of formalin-fixed paraffin-embedded blocks containing pancreatic adenocarcinomas (n = 112), neuroendocrine tumors (n = 99), serous cystadenomas (n = 28), and SPT (n = 14) as well as normal pancreas (n = 12). Immunoreactivity for DOG1 (clone K9) was assessed for intensity (1 to 3+), percentage of tumor positivity and location. Of the 99 cases of neuroendocrine tumors, only 2 (2%) were focally positive. Patchy staining was identified in 8 cases (7%) of adenocarcinoma of 1 to 2+ intensity, involving 15% to 80% of the tumor cells and primarily seen in a membranous and luminal distribution. In contrast to a previous report, no DOG1 positivity was observed in SPT, evaluated by both TMA and full sections. The TMAs of serous cystadenomas and normal pancreas were negative for DOG1. Rarely, pancreatic islets displayed granular, cytoplasmic staining. DOG1 antibody clone K9 is not a useful marker for SPT or other primary pancreatic neoplasms. Additional studies may be helpful to evaluate differences between clones of DOG1.