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Chapter 2 - University of British Columbia

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expressed in response to smoke exposure and found a subset <strong>of</strong> genes that were reversible<br />

upon smoking cessation and another subset <strong>of</strong> genes irreversible upon smoking cessation [35].<br />

Those genes which were irreversibly altered after heavy smoke exposure may have implications<br />

in affecting future risk <strong>of</strong> developing lung cancer. Moreover, these findings also suggest that<br />

when trying to identify cancer-specific changes when unmatched control samples are not<br />

available, clinical characteristics such as smoking status should be taken into consideration<br />

when comparisons are made.<br />

1.12.3 Differential gene expression analysis in lung cancer<br />

With the non-malignant, baseline gene expression defined, differential gene expression in early<br />

stages <strong>of</strong> lung cancer and locally invasive squamous cell carcinoma were then assessed [101].<br />

It was found that genes associated with epidermal development were increased in expression<br />

and mucociliary function were decreased in expression in carcinoma-in-situ as well as in<br />

precancerous stages. Finally, genes associated with tissue re-modelling were also altered in<br />

expression in local invasive cancer and also showed altered expression in carcinoma-in-situ,<br />

suggesting this function is affected early in cancer development.<br />

The Wnt pathway has been shown to be aberrant in many cancer types. At the time the study<br />

began, there were two branches <strong>of</strong> the pathway that were known to exist, canonical and non-<br />

canonical, whose activation resulted in different downstream consequences. While the<br />

canonical branch was the primary focus <strong>of</strong> most researchers studying this pathway, we sought<br />

to assess the role <strong>of</strong> the non-canonical branch in lung squamous cell carcinoma using semi-<br />

quantitative and quantitative PCR <strong>of</strong> genes which were a part <strong>of</strong> the non-canonical branch [102].<br />

From this study, it was found that (i) these non-canonical genes were expressed in the normal<br />

lung and (ii) some <strong>of</strong> these non-canonical genes were differentially expressed in tumors.<br />

An important consideration in the analysis <strong>of</strong> differential gene expression in cancer is the use <strong>of</strong><br />

suitable reference genes for data normalization. This consideration is critical to both<br />

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