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In another approach to this problem, serum collected from NSCLC patients
before treatment with gefi tinib or erlotinib were analyzed by MALDI MS and spec-
tra were acquired independently at two institutions (Taguchi et al. 2007 ). An algo-
rithm to predict outcomes after treatment with EGFR tyrosine kinase inhibitors was
developed from a training set of patients from three cohorts. The algorithm was then
tested in two independent validation cohorts of patients who were treated with gefi -
tinib and erlotinib and in three control cohorts of patients who were not treated with
EGFR tyrosine kinase inhibitors. The clinical outcomes of survival and time to pro-
gression were analyzed. This MALDI MS algorithm was not merely prognostic but
could classify NSCLC patients for good or poor outcomes after treatment with
EGFR tyrosine kinase inhibitors. This algorithm may thus assist in the pretreatment
selection of appropriate subgroups of NSCLC patients for treatment with EGFR
tyrosine kinase inhibitors. The test is commercially in development by Biodesix Inc.
One study involving EGFR mutational analysis on DNA recovered by CTC-Chip
from circulating tumor cells using allele-specifi c PCR amplifi cation has compared
the results with those from concurrently isolated free plasma DNA and from the
original tumor-biopsy specimens (Maheswaran et al. 2008 ). Thus molecular analy-
sis of circulating tumor cells from the blood of patients with lung cancer offers the
possibility of monitoring changes in epithelial tumor genotypes during the course of
treatment.
A study from Spain has evaluated the feasibility of large-scale screening for
EGFR mutations in advanced NSCLC and analyzed the association between the
mutations and the outcome of erlotinib treatment (Rosell et al. 2009 ). It concluded
that large-scale screening for EGFR mutations is feasible with subsequent custom-
ization of erlotinib and improved outcome. It is warranted in women with lung
cancer, in those who have never smoked, and in those with nonsquamous tumors.
Development of Resistance to EGFR Inhibitors
Acquired resistance to EGFR TKIs is inevitable in metastatic EGFR-mutant lung
cancers. Because RAS/RAF/MEK mutations are known mediators of acquired
resistance in other solid tumors (colon cancers, gastrointestinal stromal tumors, and
melanomas) responsive to targeted therapies, the frequency of secondary KRAS/
NRAS/BRAF/MEK1 gene mutations was analyzed in the largest collection to date
of lung cancers with acquired resistance to EGFR TKIs (Ohashi et al. 2012 ). No
recurrent NRAS, KRAS, or MEK1 mutations were found in most of patient samples
but only 1 % were found to have mutations in BRAF. Ectopic expression of mutant
NRAS or BRAF in drug-sensitive EGFR-mutant cells conferred resistance to EGFR
TKIs that was overcome by addition of a MEK inhibitor. Collectively, these positive
and negative results provide deeper insight into mechanisms of acquired resistance
to EGFR TKIs in lung cancer and should be taken into consideration in ongoing
clinical trials designed to overcome resistance. In the context of emerging knowl-
edge about mechanisms of acquired resistance to targeted therapies in various can-
cers, these data highlight that, even though solid tumors share common signaling
10 Personalized Therapy of Cancer