Not knowing all the facts about the surgery pathology leaves question what the next step is, and increase chance of recurrence or spread. In T4N0M0 oral cancer there are several ways to go, and just surgery alone is one of them, and radiation can be optional, depending on surgery, scan results, according to NCCN guidelines, if you care to look at that, but chemo alone after surgery is not listed in T4, except for for T4b, very advanced cancer, where single agent chemo treatment can be used probably due to limited choices. Everyone's situation is different, and health status has an effect on choices, and these are just guidelines.

http://oralcancerfoundation.org/treatment/pdf/head-and-neck.pdf