Several other immune checkpoint targets have been developed, such as B-cell maturation antigen (BCMA), CD19, CD20, CD47, colony-stimulating factor 1 receptor (CSF1R), indoleamine 2,3-dioxygenase (IDO), transmembrane glycoprotein mucin 1 (MUC1), New York esophageal squamous cell carcinoma 1 (NY-ESO1), stimulator of interferon genes (STING), Wilms' tumor gene 1 (WT1), human papillomavirus (HPV), T-cell immunoglobulin domain and mucin domain 3 (TIM3), etc.; however, no specific target is yet to be recognized with promising therapeutic effect in treating breast cancer [195]. This evidence concerns the gene MUC1 and breast cancer.