The structure of an epigroup with upper semimodular subepigroup lattice is described modulo groups. A special case is distinguished when this lattice belongs to a quasivariety contained in the variety of all modular lattices. It is also shown that certain properties of epigroups are invariant under taking a lattice isomorphic epigroup; this takes place, in particular, for epigroups decomposable into a semilattice of archimedean epigroups and for some types of archimedean epigroups.