Provided herein are methods for determining a subtype of a small cell lung cancer in a patient based on the express status of ASCL1, NEUROD1, and POU2F3, which are expressed in a mutually exclusive fashion. The subtype of the cancer can be used to determine the sensitivity of the cancer to certain anti-cancer therapies. As such, also provided are methods of treating patients having small cell lung cancer based on the subtyping results.