IQGAP1 in rectal adenocarcinomas: localization and protein expression before and after radiochemotherapy.

Treatment of rectal adenocarcinoma includes total mesorectal excision, which is preceded by radiochemotherapy (RCT) in cases of advanced disease. The response to RCT varies from total tumor regression to no effect but this heterogeneous response is unexplained. However, both radiation and treatment with 5-fluorouracil may induce treatment resistance through upregulation of the mitogen-activated protein kinase (MAPK) cascade. IQGAP1 is a scaffold protein that appears to be essential to MAPK signaling in cancers. We have therefore studied IQGAP1 protein expression in rectal adenocarcinomas before and after RCT. We demonstrate that cancer cells show increased apical staining for IQGAP1 following RCT. Interestingly, this increase is significantly higher in patients showing poor RCT responses. Our results also suggest that low levels of apical IQGAP1-staining in biopsies may predict the RCT response. Together, these data suggest that both the level and localization of IQGAP1 may influence the treatment response.