Sifan Yu,* Tianxiao Xu,* Jie Dai, Meng Ma, Huan Tang, Zhihong Chi, Lu Si, Chuanliang Cui, Xinan Sheng, Yan Kong, Jun Guo Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Department of Renal Cancer and Melanoma, Peking University Cancer Hospital & Institute, Beijing 100142, China *These authors contributed equally to this work Background: Asian populations are more likely to develop acral melanoma (AM) than Caucasians. The high-dose interferon (HD-IFN) α-2b regimen is the main adjuvant treatment for AM. TERT encodes the catalytic subunit of telomerase reverse transcriptase, which plays an important role in melanoma. Frequent TERT mutation and increased TERT gene expression have been described in AM. Our study aimed to investigate the status and the clinical significance of TERT copy number in a large cohort of patients with AM and to analyze the relationship between TERT copy number gain and the efficiency of HD-IFN.Patients and methods: A total of 573 melanoma samples were retrospectively collected and analyzed for TERT copy number via Sanger sequencing. Clinical data of patients were also collected.Results: TERT copy gain (copy number >2) was detected in 257 of the 573 patients with AM (44.9%). Of the 573 patients, 81 (14.1%) had a high copy gain (copy number >4). Patients with ulceration showed a significantly higher copy gain rate of TERT compared to the patients without ulceration (P=0.028). Patients with a tumor thicker than 4 mm also had a higher copy number rate of TERT than those with