Why did the wart removed from the neck for biopsy grow back?

Warts are caused by Human Papilloma Virus-infected cells growing out of control. Even though the wart was removed, it is almost impossible to remove all the infected cells, so warts have a tendency of growing back. There is no reason for concern unless the biopsy came back positive for something. If not, then all you need is a periodic removal of the wart.