Galectin‐3 and CD117 immunocytochemistry in the diagnosis of indeterminate thyroid lesions: A pilot study

Background Indeterminate thyroid lesions have always been a grey zone in the field of thyroid cytopathology. Immunocytochemistry (ICC) has emerged as a promising tool to correctly classify these indeterminate thyroid lesions into benign and malignant. Hence we planned to assess a panel of immune markers in the diagnosis of indeterminate thyroid lesions consisting of Galectin‐3, considered positive for malignancy and CD117 which is positive in benign follicular epithelial cells and negative in malignant lesions. Methods All the thyroid aspirates reported as indeterminate lesions over a period of 3 years were evaluated. Galectin‐3 and CD117 immunocytochemistry was done in 50 alcohol fixed Pap stained smears of AUS/FLUS, FN/SFN and SM category lesions. The expression of both immune markers was assessed by semi‐quantitative method and ICC score was calculated. Result Of 50 indeterminate lesions, 29 were positive for Galectin‐3 and 21 were negative. CD117 was positive in 19 cases and rests 31 were negative. With the use of this ICC panel 29/30 indeterminate lesions in which histopathological correlation was available could be recategorized correctly into benign and malignant. The combined sensitivity and specificity of Galectin‐3 and CD117 for categorising the indeterminate lesions into malignant category was 100%. Conclusion The combined use of positive and negative immune markers for thyroid malignancy increases the sensitivity and specificity of ICC to categorise the indeterminate thyroid lesions into benign and malignant. In cases with discordant ICC results we propose that inclusion of one additional positive and/or negative marker may resolve the diagnostic dilemma.