Correlation between solid papillary carcinoma and associated invasive carcinoma according to expression of WT1 and several MUCs

ObjectiveThe aim of this study was to investigate the relationship between solid papillary carcinoma (SPC) and various subtypes of associated carcinomas, including mucinous carcinoma (MC) using several immunohistochemical staining.MethodsWe grouped cases according to the subtype of the associated invasive carcinoma and the presence of an extracellular mucin component. Immunohistochemical stains for WT1 and a series of MUCs were performed to determine the agreement of immunohistochemical expression between SPC and associated carcinomas.ResultsWT1 which is characteristically expressed in MC of breast showed high expression rate (22/46, 48%) in SPC. SPCs which are associated with MC or extracellular mucin showed higher rates of WT1 (10/12, 83%, p = 0.021) and MUC2 (8/12, 67%, p = 0.002) expression, compared to SPCs which were not associated with MC or extracellular mucin. SPC and the associated MC showed good agreement in WT1 (κ = 0.857, accuracy rate = 87.5%, 7/8) with a positive expression tendency. Meanwhile, SPC and the associated invasive carcinomas other than MC showed good agreement in WT1 (κ = 1.000, accuracy rate = 100%, 9/9) with a negative expression tendency and MUC1 (κ = 0.667, accuracy rate = 77.8%, 7/9). According to these results, we could speculate that SPC showing WT1 expression tends to progress to MC, and SPC lacking WT1 expression is more likely to progress to non-MC.ConclusionSPCs can be a precursor lesion for MC and exhibit a potential to progress to other subtypes of invasive carcinoma. The status of WT1 expression in SPC could be a clue to know the direction of SPC progression, either MC or non-MC.