SPP1 and breast cancer: Multiple studies in human samples and tumor-bearing mice have shown that as a multifunctional protein, OPN expression is increased and has close relation with the occurrence, development and metastasis of laryngeal squamous cell carcinoma (Chen et al. 2015), diffuse large B-cell lymphoma (He et al. 2023), hepatocellular carcinoma (Zhu et al. 2018), etc. Notably, a previous study has shown that elevated OPN expression contributes to more aggressive behaviors of breast cancer cells and can be used as a diagnostic and prognostic marker of breast cancer (Thorat et al. 2013).