Background:
CD74, also known as the invariant chain of major histocompatibility complex class II, may function as a receptor for macrophage migration inhibitory factor (MIF). Both CD74 and MIF have been shown to have pro-tumorigenic roles in several types of cancer. A humanized anti- CD74 monoclonal antibody, milatuzumab, is under investigation in patients with hematological neoplasms. The aim of this study was to evaluate the expression of CD74 and MIF and their prognostic significance in thyroid carcinoma.

Material and Methods:
We investigated CD74 and MIF expression in thyroid cancer by immunohistochemistry. The semiquantitative scoring of the immunohistochemical staining was compared with clinicopathologic factors. Cell growth, migration, and invasion of thyroid cancer cells treated with CD74 antibody were evaluated with MTT assay, colony formation, wound healing, and transwell assay.

Result:
Cytoplasmic CD74 expression was observed in 60% papillary thyroid cancer and MIF expression in 65%. Thyroid cancer with CD74 expression exhibited larger tumor size, more extrathyroidal extension, and advanced disease stage. Treatment with CD74 antibody significantly inhibited cell growth, migration, and invasion of thyroid cancer cells. MIF expression did not correlate with clinicopathological parameters or CD74 expression.

Conclusion:
CD74 expression in thyroid cancer correlates with tumor aggressiveness. CD74 may serve as a potential therapeutic target in thyroid cancer.