Embodiments herein relate to medical devices and methods for using the same to treat cancerous tumors within a bodily tissue. A medical device system herein can include an electric field generating circuit configured to generate one or more electric fields, and control circuitry. The system can include one or more electrodes disposed on a first stimulation lead to deliver the electric fields to a site of a cancerous tumor within a patient and one or more electrodes disposed on a second stimulation lead to deliver the electric fields to the site of a cancerous tumor within a patient. The first and second stimulation leads can be configured to be implanted on or about a duodenum. The electric field generating circuit can generate electric fields at frequencies selected from a range of between 10 kHz to 1 MHz. Other embodiments are also included herein.