Embodiments herein relate to medical devices and methods for using the same to treat cancerous tumors within a bodily tissue. A medical device system is included having an electric field generating circuit configured to generate one or more electric fields and a control circuit in communication with the electric field generating circuit. The control circuit configured to control delivery of the one or more electric fields from the electric field generating circuit. The system can include two or more electrodes to deliver the electric fields to a site of a cancerous tumor within a patient and a temperature sensor to measure the temperature of tissue at the site of the cancerous tumor. The control circuit can cause the electric field generating circuit to generate one or more electric fields at frequencies selected from a range of between 10 kHz to 1 MHz. Other embodiments are also included herein.