Lung cancer is the most common and lethal malignancy, with lung adenocarcinoma accounting for approximately 40% of all cases. Despite some progress in understanding the pathogenesis of this disease and developing new therapeutic approaches, the current treatments for lung adenocarcinoma remain ineffective due to factors such as high tumour heterogeneity and drug resistance. Therefore, there is an urgent need to identify novel therapeutic targets. Calcyclin-binding protein (CacyBP) can regulate a variety of physiological processes by binding to different proteins, but its function in lung adenocarcinoma is unknown. Here, we show that CacyBP is highly expressed in lung adenocarcinoma tissues, and high CacyBP expression correlates with poorer patient survival. Moreover, overexpression of CacyBP promoted the proliferation, migration and invasion of lung adenocarcinoma cell lines. Further mechanistic studies revealed that CacyBP interacts with the tumour suppressor ovarian tumour (OTU) deubiquitinase 5 (OTUD5), enhances the ubiquitination and proteasomal degradation of OTUD5 and regulates tumourigenesis via OTUD5. In conclusion, our study reveals a novel mechanism by which CacyBP promotes tumourigenesis by increasing the ubiquitination level and proteasome-dependent degradation of OTUD5, providing a potential target for the treatment of lung adenocarcinoma.