Through the query of the database GEPIA2, the expression of RPS21 gene is not significantly different in tumor and normal tissues (Supplementary Figure 2C), so its potential function in breast cancer has not been studied so far, but according to our research, one of the transcripts of RPS (AA- RPS21) is differentially expressed in cancer and normal tissues of breast cancer patients, which suggests that this transcript may play a tumor-driving role in breast cancer, so it is worthy of further investigation. The gene discussed is RPS21; the disease is cancer.