Patients receive an initial loading dose of trastuzumab IV over 90 minutes on day 1 of the first week and a maintenance dose of trastuzumab IV over 30-90 minutes on day 1 of each subsequent week. Patients receive IL-12 IV on days 2 and 5 beginning on week 3. Treatment with maintenance trastuzumab and IL-12 repeats weekly for 14 weeks in the absence of disease progression or unacceptable toxicity. Patients with stable or responding disease continue treatment for up to 38 additional weeks.