Although B-Raf V600E is the most common somatic mutation in papillary thyroid carcinoma (PTC), how it induces tumor aggressiveness is not fully understood. Using gene set enrichment analysis and in vitro and in vivo functional studies, we identified and validated a B-Raf V600E gene set signature associated with tumor progression in PTCs. An independent cohort of B-Raf V600E -positive PTCs showed significantly higher expression levels of many extracellular matrix genes compared with controls. We performed extensive in vitro and in vivo validations on thrombospondin-1 (TSP-1), because it has been previously shown to be important in the regulation of tumor angiogenesis and metastasis and is present in abundance in tumor stroma. Knockdown of B-Raf V600E resulted in TSP-1 downregulation and a reduction of adhesion and migration/invasion of human thyroid cancer cells. Knockdown of TSP-1 resulted in a similar phenotype. B-Raf V600E cells in which either B-Raf V600E or TSP-1 were knocked down were implanted orthotopically into the thyroids of immunocompromised mice, resulting in significant reduction in tumor size and fewer pulmonary metastases from the primary carcinoma as compared with the control cells. Treatment of orthotopic thyroid tumors, initiated 1 week after tumor cell implantation with PLX4720, an orally available selective inhibitor of B-Raf V600E , caused a significant tumor growth delay and decreased distant metastases, without evidence of toxicity. In conclusion, B-Raf V600E plays an important role in PTC progression through genes (i.e., TSP-1) important in tumor invasion and metastasis. Testing of a patient's thyroid cancer for B-Raf V600E will yield important information about potential tumor aggressiveness and also allow for future use of targeted therapies with selective B-Raf V600E inhibitors, such as PLX4720. extracellular matrix | metastasis | papillary thyroid cancer | tumor microenvironment | cell invasion P apillary thyroid cancer (PTC), with its incidence increasing by almost 5% each year, currently ranks as the eighth most common malignancy diagnosed in women (1). Neck recurrences alone are responsible for a third of thyroid cancer-related deaths. There is no effective treatment for radioiodine-resistant metastatic disease; the 10-year survival rate in these cases is only 10% (2). Molecular understanding of the aggressive clinical behavior of this subset of patients is needed to develop new therapeutic options.

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Background: Orthotopic mouse models of human cancer represent an important in vivo tool for drug testing and validation. Most of the human thyroid carcinoma cell lines used in orthotopic or subcutaneous models are likely of melanoma and colon cancer. Here, we report and characterize a novel orthotopic model of human thyroid carcinoma using a unique thyroid cancer cell line. Methods: We used the cell line 8505c, originated from a thyroid tumor histologically characterized by anaplastic carcinoma cell features. We injected 8505c cells engineered using a green fluorescent protein-positive lentiviral vector orthotopically into the thyroid of severe combined immunodeficient mice. Results: Orthotopic implantation with the 8505c cells produced thyroid tumors after 5 weeks, showing large neck masses, with histopathologic features of a high-grade neoplasm (anaplasia, necrosis, high mitotic and proliferative indexes, p53 positivity, extrathyroidal invasion, lymph node and distant metastases) and immunoprofile of follicular thyroid cell origin with positivity for thyroid transcription factor-1 and PAX8, and for cytokeratins. Conclusions: Here we describe a novel orthotopic thyroid carcinoma model using 8505c cells. This model can prove to be a reliable and useful tool to investigate in vivo biological mechanisms determining thyroid cancer aggressiveness, and to test novel therapeutics for the treatment of refractory or advanced thyroid cancers.

Purpose: Targeting mutations leading to PI3K/mTOR/Akt activation are of interest in thyroid cancer (TC). We evaluated the efficacy of everolimus in aggressive, radioactive iodine refractory (RAIR) TC and correlated tumor mutational profiling with response. Exploratory medullary and anaplastic TC cohorts were included.Experimental Design: This single-arm, multi-institutional phase II study was conducted from 2009-2013 in patients with incurable RAIR TC who had radiographic progression six months prior to enrollment. The primary endpoint was progression-free survival (PFS) with a median follow-up of 31.8 months. The study is closed to enrollment but treatment and follow-up are ongoing. A targeted next-generation sequencing platform was used for mutational analysis.Results: Thirty-three patients with differentiated TC (DTC), 10 with medullary TC (MTC), and 7 with anaplastic TC (ATC) enrolled. For the DTC cohort, median PFS was 12.9 months (95% CI, 7.3-18.5) with a 2-year PFS of 23.6% (95% CI, 10.5-39.5). Median OS was not reached; 2-year OS was 73.5% (95% CI, 53.8-85.8). Among ATC patients, 1 had a partial response and was progression-free until 17.9 months post study entry and one had disease stability for 26 months, respectively. The genomically profiled cohort enriched for PI3K/mTOR/Akt alterations. PI3K/mTOR/Akt mutated ATC subgroups appeared to benefit from everolimus. Treatmentrelated adverse events were as anticipated. Conclusion:Everolimus has significant anti-tumor activity in TC. While genomic profiling does not currently guide therapeutic selection in TC patients, these data have important implications when considering the use of an mTOR inhibitor in an era of precision medicine.

Purpose B-RafV600E may play a role in the progression from papillary thyroid cancer to anaplastic thyroid cancer (ATC). We tested the effects of a highly selective B-RafV600E inhibitor, PLX4720, on proliferation, migration, and invasion both in human thyroid cancer cell lines (8505cB-RafV600E and TPC-1RET/PTC-1 and wild-type B-Raf) and in primary human normal thyroid (NT) follicular cells engineered with or without B-RafV600E. Experimental Design Large-scale genotyping analysis by mass spectrometry was performed in order to analyze >900 gene mutations. Cell proliferation and migration/invasion were performed upon PLX4720 treatment in 8505c, TPC-1, and NT cells. Orthotopic implantation of either 8505c or TPC-1 cells into the thyroid of severe combined immunodeficient mice was performed. Gene validations were performed by quantitative polymerase chain reaction and immunohistochemistry. Results We found that PLX4720 reduced in vitro cell proliferation and migration and invasion of 8505c cells, causing early downregulation of genes involved in tumor progression. PLX4720-treated NT cells overexpressing B-RafV600E (heterozygous wild-type B-Raf/B-RafV600E) showed significantly lower cell proliferation, migration, and invasion. PLX4720 treatment did not block cell invasion in TPC-1 cells with wild-type B-Raf, which showed very low and delayed in vivo tumor growth. In vivo, PLX4720 treatment of 8505c orthotopic thyroid tumors inhibited tumor aggressiveness and significantly upregulated the thyroid differentiation markers thyroid transcription factor 1 and paired box gene 8. Conclusions Here, we have shown that PLX4720 preferentially inhibits migration and invasion of B-RafV600E thyroid cancer cells and tumor aggressiveness. Normal thyroid cells were generated to be heterozygous for wild-type B-Raf/B-RafV600E, mimicking the condition found in most human thyroid cancers. PLX4720 was effective in reducing cell proliferation, migration, and invasion in this heterozygous model. PLX4720 therapy should be tested and considered for a phase I study for the treatment of patients with B-RafV600E ATC.

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In addition to predicting cancer prevalence, the TBS also imparts important prognostic information about cancer type, variant, and risk of recurrence. These data extend the utility of TBS classification by fostering an improved understanding of the risk posed by any confirmed malignancy.