Hypoxia-Associated Marker CA IX Does Not Predict the Response of Locally Advanced Rectal Cancers to Neoadjuvant Chemoradiotherapy.

Hypoxia-associated proteome changes have been shown to be associated with resistance to chemo-and radiotherapy. Our study evaluated the role of the hypoxia-inducible (HIF)-1 target gene carbonic anhydrase (CA) IX in the prediction of the response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer (stages II and III). A total of 29 pretreatment biopsy specimens were stained for CA IX by immunohistochemistry, converted to digital images and evaluated in a quantitative fashion using image analysis software. Contrary to our expectations, a trend towards a correlation between better tumor regression (> 50 %) and higher expression of CA IX (p = 0.056) was found. CA IX was also present more frequently in pathological tumor stage T1 (pT1) tumors (p = 0.048). Conversely, no association with lymph node metastasis was identified. In conclusion, as a single marker, CA IX expression is not able to identify a hypoxia-related treatment resistant phenotype in rectal cancer.