Thus, the HTM model facilitates the analysis of antibody-based and immunomodulatory tumor treatments under unique “human-like conditions.” We utilized two HER2 overexpressing BC cell lines and generated a BT474- and a SK-BR-3- based TM (w/o a human immune system) and HTM (humanized with hematopoietic stem cells), in which solid tumor growth and tumor cell effusion developed, respectively. The gene discussed is ERBB2; the disease is neoplasm.