  The quark mass dependence of hadrons is an important input for lattice
calculations. We investigate the light quark mass dependence of the binding
energy of the X(3872) in a finite box to next-to-leading order in an effective
field theory for the X(3872) with perturbative pions (XEFT). At this order, the
quark mass dependence is determined by a quark mass-dependent contact
interaction in addition to the one-pion exchange. While there is only a
moderate sensitivity to the light quark masses in the region up to twice their
physical value, the finite volume effects are significant already at box length
as large as 20 fm.
