U.S. trademark rights are based upon use and a trademark registration is subject to cancelation based upon prior use up until it achieves incontestible status as a result of 5 years of continuous and exclusive use. If by a few years, you mean less than 5, your registration is certainly capable of being canceled based upon prior use by another. Cancelation proceedings can be very expensive.
Answered on Dec 07th, 2011 at 3:42 PM