The invention provides a method for treating cancer using a coadministration strategy that combines local codelivery of a therapeutic agent and an intracellular penetration enhancing agent, and optionally in further combination with local administration of an immunotherapeutic agent, such as a cancer vaccine or NKT agonist. The invention also provides a method for treating cancer using an intracellular penetration enhancing agent. The methods of the invention aim to substantially kill and/or destroy the target tumor cells, as well as those cancerous cells that have metastasized to other parts of the body.