PDCD1 and breast carcinoma: Immunotherapy for breast cancer brain metastasis is also under investigation in many clinical trials using haploidentical hematopoietic stem cells, cytotoxic lymphocytes, a dendritic vaccine, and dendritic cells (NCT01782274 and NCT03638765), durvalumab (anti-PD-1 antibody—NCT04711824), and bintrafusp alfa (targeting PD-1—NCT04789668).