A score based on microscopic criteria proposed for analysis of papillary carcinoma of the thyroid

Morphologic examination is the gold standard for diagnosing papillary thyroid carcinoma (PTC). This diagnosis, especially for the follicular variant, may be variable even among experts. Our objective was to analyze the frequency of PTC microscopic criteria in a series of thyroid tumors including follicular adenoma (FA) and PTC to build a score which could constitute a novel way for microscopic analysis of such thyroid tumors. Sixty-six PTC and 66 FA were matched for age, sex, and thyroiditis. Two independent observers delineated the classical PTC microscopic criteria. PTC microscopic criteria were variably expressed in individual tumors. Under univariate analysis, all criteria were significantly more frequent in PTC than in FA (p<0.05). Under multivariate analysis, the most important criteria were: dark staining colloid >25%, nuclear grooves, enlarged nuclei, ovoid nuclei >5% of tumor cells, and lack of polarization. Using linear discriminant analysis, these five criteria allowed us to build a scaled score. The score proposed did not allow the making of a definite distinction between FA and PTC in routine practice. It represents the variety of microscopic presentations of FA and PTC on the basis of a statistical analysis and could help in further evaluation of immunohistochemical or molecular markers.