Several lines of evidence have shown that long non-coding RNAs (lncRNAs) are dysregulated in many diseases. nevertheless, the biological relevance of the lncRnAs in papillary thyroid carcinoma (ptc) has not been fully explored. We demonstrated that CTC was a negative regulator of PTC cell migration and invasion in vitro and in vivo. We found that microRNA-146 (miR-146) is an inhibitory target of CTC. We then demonstrated that CTC functioned as a miR-146 decoy to de-repress expression of KIT. Further study demonstrated that CTC modulated the progression and chemoresistance of PTC cells via miR-146 and KIT. The analysis of hundreds of clinical specimens revealed that CTC and KIT levels were downregulated, whereas miR-146 levels were greater in PTC tissues than in normal thyroid. Their expression levels correlated with one another. In conclusion, CTC functions as a competing endogenous RNA to inhibit the progression and chemoresistance of PTC cells, and identifies CTC serve as a potential therapeutic agent to suppress PTC progression. Thyroid carcinomas represent the majority of endocrine neoplasms worldwide, and their incidence has increased steadily over the past decade 1-3. Thyroid cancers can be classified as three types: well-differentiated, poorly differentiated and anaplastic carcinomas 4,5. Papillary thyroid carcinoma (PTC) is a well-differentiated type, accounting for 70-80% of thyroid carcinomas 4,5. Through surgical removal, thyroid hormone and adjuvant radioactive iodine therapy, PTC has a favorable prognosis 6. Nevertheless, some patients exhibit aggressive behavior due to metastases 6. Therefore, identification of potential biomarkers and therapeutic targets could aid the therapy of PTC. The non-coding RNA (ncRNA) refers to RNA molecules that cannot encode proteins, but nevertheless have biological functions 7,8. These ncRNAs has many types, including microRNAs, snoRNAs and longer transcripts 9,10. Long non-coding RNAs (LncRNAs) (>200 nt) are a newly-described class of RNA transcripts which had been regard as "transcriptional noise" in the past 11,12. Nevertheless, several lines of data support the notion that particular lncRNAs function as crucial regulators in the cancer biology, rather than "nonsense fragments" 13-15. For PTC, many functional lncRNAs have been characterized, including ATB, CASC2, H19, and NEF, suggesting that lncRNAs may be able to be diagnostic tags and potential therapeutic targets 16-20. MircroRNAs (miRNAs) are noncoding RNA molecules in 18-25 nucleotides length that negatively regulate gene expression at the post-transcriptional level 21,22. miRNAs regulate proliferation, metastasis and apoptosis by inhibiting tumor suppressor gene pathways or activating oncogenic pathways 23. Almost half of human miRNAs are in the position of fragile sites and genomic regions that are associated with cancers 24. Nevertheless, little is known about the biological role of miRNAs in PTC. A recent study reported that miR-146, miR-221 and miR-222 were upregulated in PTC compared to levels in adjacen...