Highly sensitive detection of EGFR T790M mutation using colony hybridization predicts favorable prognosis of patients with lung cancer harboring activating EGFR mutation.
BACKGROUND
Approximately 50% of lung cancer patients with epidermal growth factor receptor (EGFR)-mutations (deletion in exon 19 or L858R) who develop acquired resistance to EGFR tyrosine kinase inhibitors (TKIs) reportedly carry a secondary EGFR T790M mutation. This mutation has been suggested to be present in tumor cells before EGFR-TKI treatment in a small population of individuals. Here, we use a highly sensitive colony hybridization technique in an attempt to evaluate the actual incidence of T790M in pretreatment tumor specimens.


METHODS
DNA was extracted from surgically resected tumor tissues of 38 patients with the EGFR mutation and examined for the presence of T790M, using a standard polymerase chain reaction based method followed by a modified colony hybridization (CH) technique with an analytical sensitivity of approximately 0.01%. Associations between the T790M status and clinical characteristics including time to treatment failure (TTF) for EGFR-TKI were evaluated.


RESULTS
The T790M mutation analysis of the specimens from the 38 patients detected 30 mutants (79%). The median TTF was 9 months for the patients with pretreatment T790M and 7 months for the patients without the T790M mutation (p = 0.44). When the patients with T790M were divided into strongly positive and modestly positive subgroups in terms of the frequency of positive signals observed using CH technique, the 7 patients with strong positivity had a TTF that was significantly longer than that of the 8 patients without T790M (p = 0.0097) and of the 23 patients with modest positivity (p = 0.0019).


CONCLUSIONS
Our highly sensitive CH method showed that a subgroup of non-small-cell lung cancer patients with the EGFR mutation harbored the rare T790M allele before EGFR-TKI treatment. A high proportion of T790M allele may define a clinical subset with a relatively favorable prognosis.
Department of Genome Biology, Kinki University School of Medicine, Osaka, Japan.
Yoshihiko
Y
Fujita
Kenichi
K
Suda
Hideharu
H
Kimura
Kazuko
K
Matsumoto
Tokuzo
T
Arao
Tomoyuki
T
Nagai
Nagahiro
N
Saijo
Yasushi
Y
Yatabe
Tetsuya
T
Mitsudomi
Kazuto
K
Nishio
D000230:Adenocarcinoma / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D015331:Cohort Studies; D004252:DNA Mutational Analysis; D004273:DNA, Neoplasm / Q000235:genetics; D066246:ErbB Receptors / Q000235:genetics*; D005260:Female; D006801:Humans; D006824:Hybridization, Genetic; D008175:Lung Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D009367:Neoplasm Staging; D016133:Polymerase Chain Reaction; D011379:Prognosis; D012680:Sensitivity and Specificity; D015996:Survival Rate; D061665:Time-to-Treatment
D004273:DNA, Neoplasm; C512478:EGFR protein, human; D066246:ErbB Receptors