multiple different types of cancer
have identifi ed different subtypes
that are not clearly defi ned
by genetic abnormalities, and
thus may be defi ned by epigenetic
mechanisms ( 13). Indeed, Friedmann-
Morvinski et al. show that
specifi c subtypes of mouse GBM
are developed on the basis of the
cell of origin. Further studies are
required in multiple cancers to
determine the extent to which the
cell of origin infl uences epigenetic
heterogeneity.
As our understanding of cancer
genetics broadens, the opportunities
to apply that knowledge to
individualize therapy for cancer
patients with more targeted therapies
will continue to increase as
well. However, molecularly targeted
therapies have shown that
cancers are remarkably adept at
developing resistance, and some
of the mechanisms of resistance
are likely a result of either preexisting
(cancer stem cells) or
acquired (adaptation) epigenetic
differences. These studies
raise the possibility that infl uencing
the epigenetic state of cancer
cells may sensitize cancers to concurrent
treatments and/or restrict cancer cell adaptation
to therapeutic intervention (see the fi gure).
Emerging classes of therapeutics aimed
at enzymes that catalyze chemical modifi -
cations of DNA and chromatin-associated
proteins (and thereby modify the epigenetic
states of cells) are currently entering clinical
trials ( 14). There is hope that a combination
of therapies that target genetic abnormalities,
epigenetic properties, immune mechanisms,
and resistance to programmed cell death
(apoptosis) will usher in better treatments to
deal with diffi cult-to-cure cancers like GBM