Methods for treating a subject with a cancer that is characterized by overexpression of HER2 receptor protein using a combination of interleukin-2 (IL-2) or variant thereof and at least one anti-HER2 antibody or fragment thereof are provided. These anti-tumor agents are administered as two separate pharmaceutical compositions, one containing IL-2 (or variant thereof), the other containing at least one anti-HER2 antibody (or fragment thereof), according to a dosing regimen. Administering of these two agents together potentiates the effectiveness of the anti-HER2 antibody alone, resulting in a positive therapeutic response that is improved with respect to that observed with this anti-tumor agent.