NPC2 expression in thyroid tumors and its possible diagnostic utility

Histopathologic diagnosis of thyroid lesions is sometimes difficult and may require the assistance of immunohistochemistry. Currently-used immunohistochemical biomarkers share the weakness of staining both papillary thyroid carcinoma and other non-papillary thyroid lesions. We examined NPC2 as an immunohistochemical marker in various thyroid lesions to determine the subcellular localization of the immunohistochemistry signal and evaluated the value of NPC2 as a diagnostic marker of papillary thyroid carcinoma. NPC2 immunostaining was performed on various thyroid tumors and tumor-like lesions. The immunostaining revealed significantly different patterns for papillary carcinomas and the other lesions. Papillary carcinomas exhibited moderate to strong granular cytoplasmic staining, often with basal membranous accentuation. In contrast, the other lesions showed mostly weak cytoplasmic staining, often with apical membranous accentuation. The subcellular localization of NPC2 provided insight into contrasting histopathologic morphology and reversed cellular polarity between the papillary patterns of papillary carcinomas and the follicular patterns of non-papillary carcinoma lesions. The diagnostic characteristics of NPC2 immunohistochemistry for non-follicular papillary carcinomas versus non-papillary carcinoma lesions were a sensitivity of 97.3%, specificity of 96.9%, positive predictive value of 94.7%, and negative predictive value of 98.4%. Significant differences were present between the two staining patterns in papillary carcinoma relative to mean age, nodal metastasis, and follicular and non-follicular variants (P = 0.02, P = 0.03, and P = 0.000, respectively). In conclusion, our evaluation of the subcellular localization of NPC2 using immunohistochemistry demonstrated possible value of NPC2 as a biomarker and provided insight into the morphologic characteristics of papillary carcinoma.