Imp3 expression in benign and malignant thyroid tumors and hyperplastic nodules

IMP3, a member of insulin-like growth factor II m RNA binding protein family, seems to be promising in the diagnosis of carcinomas of many organs as well as malignant melanomas and some sarcomas. It is postulated that it might be a marker of malignancy. The results of the few prior studies indicate that IMP3 has the potential to be useful in distinguishing benign and malignant tumors of thyroid.

We aimed to evaluate the immunohistochemical expression of IMP3 in non-neoplastic nodules and benign and malignant tumors of the thyroid.

Diagnostic accuracy study.

Overall, 92 thyroid lesions, including 22 nodular hyperplasia (NH), 14 follicular adenoma (FA), 9 follicular carcinoma (FC), 37 papillary carcinoma (PC) (15 follicular variant), 3 well differentiated carcinoma-not otherwise specified (WDC-NOS), 4 poorly differentiated carcinoma (PDC) and anaplastic carcinoma (AC) were included. Immunohistochemically, cytoplasmic expression of IMP3 was evaluated in terms of extent and intensity of the staining semi-quantitatively and an immunohistochemical score (IHS) was obtained for each case. A score higher than 2 was considered positive staining.

In contrast with previous studies, we observed positive staining in benign lesions, especially in benign tumors. For identifying malignant tumors, the sensitivity of IMP3 was 82.1%, specificity was 33.3%, positive predictive value (PPV) was 65.7% and negative predictive value (NPV) was 54.5%. In distinguishing neoplastic and hyperplastic lesions, the sensitivity was 50%, specificity was 15.7%, PPV was 15.7% and NPV was 50%. The IMP3 expression was similar for FA and well differentiated carcinomas (p=0.434), but there was a significant difference between hyperplastic nodules and FA (p=0.011).

Our data suggest that IMP3 is effective in discriminating hyperplastic and neoplastic lesions but not useful in differentiating benign tumors from malignant tumors.