Why can an epidermoid tumor regrow after being removed?

Incomplete margins: The regrowth of epidermoid carcinoma usually represents a failure to obtain proper margins or treat adequate margins that may be within a field effect where normal appearing cells are in the process of transforming. As such epidermoid Ca of anus, oral cavity, cervix may be seen to have post surgical recurrence unless measures taken such as adjuvant radiation and chemotherapy are employed.