Breast cancer remains the most common malignancy and the leading cause of cancer?associated mortality in women worldwide. Lysosomal protein transmembrane 5 (LAPTM5), a lysosomal membrane protein, plays an important role in several human malignancies. However, the biological functions and mechanism of LAPTM5 in breast cancer remain unclear. In the present study, the potential tumor?promoting effect of LAPTM5 was predicted by bioinformatics analysis. LAPTM5 was highly expressed in breast cancer clinical specimens. Moreover, studies demonstrated that cell proliferation, migration and invasion, as well as the process of epithelial?mesenchymal transition (EMT) were promoted by LAPTM5 overexpression and were suppressed by LAPTM5 downregulation . The tumor?promoting effects of LAPTM5 were also confirmed by xenograft tumor assay . It was found that the tumor?promoting effects of LAPTM5 were partly dependent on the activation of the Wnt/β?catenin signaling pathway. Furthermore, dual?luciferase and chromatin immunoprecipitation assays verified that the transcription factor forkhead box protein 3 (FOXP3) directly bound to the promoter of LAPTM5 and negatively regulated its expression. Taken together, the present findings indicated that LAPTM5, negatively regulated by FOXP3, promoted the malignant phenotypes of breast cancer through activating the Wnt/β?catenin signaling pathway.