ity, from a genetic standpoint, for
the majority of driver mutations,
I would say we don’t detect significant heterogeneity.
For example, KRAS mutations
in colon cancer are present in all the tumor
cells, and when the tumors metastasize, they
are present in all the tumor cells. We’ve analyzed
in the molecular diagnostics lab many
lung cancers over the past 5 years; we know
EGFR [epidermal growth factor receptor]
mutations or ALK [anaplastic lymphoma
kinase] translocations are present in all of
the tumor cells, both pre- and post-therapy.
Even if a patient develops resistance to a targeted
therapy, those drivers are still there.
So in practice the important drivers are not
heterogeneous. But recently I’ve started to
change my mind.
Analysis of receptor tyrosine kinase gene
amplifications in glioblastoma [Cancer Cell,
20, 810–817, 2011] has really altered how I
think about the genetics of tumors in general.
We observed that there is substantial genetic
heterogeneity at the copy number level from
cell to cell. Within single tumors, we see
intermixed populations of tumor cells with
distinct genetics, one cell next to another
next to another with three different genetic
drivers; one cell with MET amplification, one
with EGFR amplification, one with PDGFR
[platelet-derived growth factor receptor a]
amplification. These observations suggested
to us that it is possible that tumor cell populations
may subspecialize and begin to support
each other.
Robert M. Hoffman: Another way to
think about heterogeneity within a single
tumor mass is heterogeneity in terms of cell
division. For example, using the FUCCI
system [Invitrogen, Carlsbad, CA, USA],
which reports what phase of the cell cycle
a cell may be in—resting cells express red
fluorescent protein and dividing cells express
a green fluorescent protein—[my] group has