Biomedical Engineering Reference
In-Depth Information
with high sensitivity and specificity [46]. Many researchers have
had difficulty in detecting ALK fusion proteins by IHC in lung
adenocarcinomas likely due to instability of
or due to
weak transcriptional activity of the promoter-enhancer region of
EML4
EML4-ALK
compared with that of the
NPM
promoter [33]. As a result,
over 30% of
rearranged lung adenocarcinomas are not detected
by standard immunohistochemistry. In one study using standard
protocols, only 40% of the FISH-confirmed ALK rearranged lung
adenocarcinomas stained positively for ALK fusion proteins.
However, by adding an amplification step with tyramide to the
protocol, that number improved to 80% [41]. Similarly, another
study has shown an even higher sensitivity with the addition of an
intercalated antibody-enhanced polymer to the standard antibodies
[28, 48]. Despite the addition of these amplification steps though,
there are still a number of false negatives. Recently, Mino-Kenudson
et al.
ALK
reported a new immunohistochemical assay with novel rabbit
monoclonal antibodies (clones D5F3 and D9E4; Cell Signaling
Technology, Danvers, MA) with higher sensitivity for ALK protein
expression than the conventional mouse monoclonal antibody (clone
ALK1; Dako USA) [49]. Their test was both highly sensitive (100%)
and highly specific (99%) as ALK protein expression was detected
in all of the 22
-rearranged lung adenocarcinomas and was not
detected in the 131 non-
ALK
rearranged lung adenocarcinomas [49].
In 13 of the 22 cases positive for
ALK
rearrangements (59%), the ALK
protein expression could only be detected with the novel antibodies.
They were also able to show that the ALK protein expression was
much lower in
ALK
ALK
rearranged NSCLC then compared with
ALK
rearranged anaplastic large cell lymphoma thus accounting for the
reduced sensitivity of conventional immunohistochemistry [49].
These results support the potential role for immunohistochemistry
in detecting
ALK
rearrangements in NSCLC.
16.4.3
Fluorescence
in situ
Hybridization Based
Detection
A more specific way to detect
ALK
rearrangements is by using
fluorescence
in situ
hybridization (FISH) of probes that flank the
ALK
fusion point. FISH has been performed with the commercially
