CD44 Variant Expression in Follicular Cell-Derived Thyroid Cancers: Implications for Overcoming Multidrug Resistance

Thyroid cancer (TC) is a significant global health issue that exhibits notable heterogeneity in incidence and outcomes. In low-resource settings such as Africa, delayed diagnosis and limited healthcare access exacerbate mortality rates. Among follicular cell-derived thyroid cancers-including papillary (PTC), follicular (FTC), anaplastic (ATC), and poorly differentiated (PDTC) subtypes-the role of CD44 variants has emerged as a critical factor influencing tumor progression and multidrug resistance (MDR). CD44, a transmembrane glycoprotein, and its splice variants (CD44v) mediate cell adhesion, migration, and survival, contributing to cancer stem cell (CSC) maintenance and therapy resistance. Differential expression patterns of CD44 isoforms across TC subtypes have shown diagnostic, prognostic, and therapeutic implications. Specifically, CD44v6 expression in PTC has been correlated with metastasis and aggressive tumor behavior, while in FTC, its expression aids in distinguishing malignant from benign lesions. Furthermore, CD44 contributes to MDR through enhanced drug efflux via ABC transporters, apoptosis evasion, and CSC maintenance via the Wnt/β-catenin and PI3K/Akt pathways. Targeted therapies against CD44 such as monoclonal antibodies, hyaluronic acid-based nanocarriers, and gene-editing technologies hold promise in overcoming MDR. However, despite the mounting evidence supporting CD44-targeted strategies in various cancers, research on this therapeutic potential in TC remains limited. This review synthesizes existing knowledge on CD44 variant expression in follicular cell-derived thyroid cancers and highlights potential therapeutic strategies to mitigate MDR, particularly in high-burden regions, thereby improving patient outcomes and survival.