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OBJECTIVE Persistent efforts have been made to promote clinical trial transparency, which included encouraging trial registration and prospective registration, as well as protocol disclosure. This study aims to analyze the extent of registration, prospective registration and protocol disclosure in oncology clinical trials and their changing trends. STUDY DESIGN AND SETTING All phase II and phase III oncology clinical trials published in 5 major journals, Annals of Oncology, Journal of Clinical Oncology, JAMA Oncology, Lancet Oncology and New England Journal of Medicine, between January 2013 and December 2017, were included. Data on trial characteristics as well as registration status and availability of protocol and its location were collected. RESULTS In total, 625 articles were included, 92% were registered, of which 76% were prospectively registered. Overall, 27% provided protocols. Increasing trends were observed in registration, prospective registration and protocol disclosure (all P < 0.001). Studies with enrollment number larger than median number were more likely to be registered (adjusted odds ratio (aOR), 3.14 [95% confidence interval (CI), 1.21 - 8.15]), and to provide protocols (aOR, 3.84 [95% CI, 2.24 - 6.57]) than those with smaller enrollment number. Studies with non-industry funding was less likely to be prospectively registered (aOR, 0.37 [95% CI, 0.25 - 0.55]) but more likely to provide protocols (aOR, 1.69 [95% CI, 1.13 - 2.52]) compared to those with industry funding only. CONCLUSION Although the rates of registration, prospective registration and protocol disclosure Conclusion Although the rates of registration, prospective registration and protocol disclosure of oncology trials have significantly increased over the years, there is still room for improvement.