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

OBJECTIVE: The 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.

METHODS: We 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.

RESULTS: WT1 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.

CONCLUSION: SPCs 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.