  PSR B1259-63/LS 2883 is a very high energy (VHE; $E > 100$ GeV) {\gamma}-ray
emitting binary consisting of a 48 ms pulsar orbiting around a Be star with a
period of $\sim3.4$ years. The Be star features a circumstellar disk which is
inclined with respect to the orbit in such a way that the pulsar crosses it
twice every orbit. The circumstellar disk provides an additional field of
target photons which may contribute to inverse Compton scattering and
{\gamma}{\gamma}-absorption, leaving a characteristic imprint in the observed
spectrum of the high energy emission. At GeV energies, the source was detected
for the first time during the previous periastron passage which took place on
December 15, 2010. The Fermi Large Area Telescope (LAT) reported a spectacular
and unexpected {\gamma}-ray flare occurring around 30 days after periastron and
lasting for about 7 weeks. In this paper, we study the signatures of
Compton-supported, VHE {\gamma}-ray induced pair cascades in the circumstellar
disc of the Be star and their possible contribution to the GeV flux. We show
that cascade emission generated in the disk cannot be responsible for the GeV
flare, but it might explain the GeV emission observed close to periastron. We
also show that the {\gamma}{\gamma}-absorption in the disk might explain the
observed TeV light curve.
