Human Cancer Biology Activationof themTORPathway inPrimaryMedullary Thyroid Carcinoma and Lymph Node Metastases

Purpose: Understanding the molecular pathogenesis of medullary thyroid carcinoma (MTC) is prerequisite to the design of targeted therapies for patients with advanced disease. Experimental Design:We studied by immunohistochemistry the phosphorylation status of proteins of the RAS/MEK/ERK and PI3K/AKT/mTOR pathways in 53 MTC tissues (18 hereditary, 35 sporadic), including 51 primary MTCs and 2 cases with only lymph node metastases (LNM). We also studied 21 autologous LNMs,matched to 21 primaryMTCs. Stainingwas graded on a 0 to 4 scale (S score) based on the percentageof positive cells.Wealso studied the functional relevanceof themTORpathwaybymeasuring cell viability, motility, and tumorigenicity upon mTOR chemical blockade. Results: Phosphorylation of ribosomal protein S6 (pS6), a downstream target of mTOR, was evident (S 1) in 49 (96%) of 51 primary MTC samples. This was associated with activation of AKT (phosphoSer473, S > 1) in 79% of cases studied. Activation of pS6 was also observed (S 1) in 7 (70%) of 10 hereditary C-cell hyperplasia specimens, possibly representing an early stage of C-cell transformation. It is noteworthy that 22 (96%)of 23LNMshad ahighpS6positivity (S 3),whichwas increased comparedwith autologous matched primary MTCs (P 1⁄4 0.024). Chemical mTOR blockade blunted viability (P < 0.01), motility (P < 0.01), and tumorigenicity (P < 0.01) of human MTC cells. Conclusion: The AKT/mTOR pathway is activated in MTC, particularly, in LNMs. This pathway sustains malignant features of MTC cell models. These findings suggest that targeting mTORmight be efficacious in patients with advanced MTC. Clin Cancer Res; 18(13); 3532–40. 2012 AACR.