ERK signaling in colorectal cancer: a preliminary report on the expression of phosphorylated ERK and the effects of radiation therapy.

OBJECTIVES Phosphorylated extracellular signal-regulated kinase (ERK) activates cell survival pathways and may promote tumor cell proliferation. The purpose of this study was to determine the level of phospho-ERK staining in pretreatment specimens, and the effect of a short course of radiation therapy (RT) on the levels of phospho-ERK in specimens of colorectal cancer. METHODS Specimens of colorectal tumors were obtained from patients beginning RT before surgery. Tumors were graded and histologically staged. Subsequently, tumor samples were reacted with antiphospho-ERK antibodies and the level of staining intensity was assessed. RESULTS Of the 12 subjects evaluated, 7 of 12 had tumors that positively stained for phospho-ERK before and/or after RT. Most patients who were phospho-ERK positive before RT converted to ERK negativity after RT. CONCLUSIONS The results of this pilot study indicate that phospho-ERK levels may serve as a prognostic marker in colorectal cancer, and further studies are warranted to determine how changes in phospho-ERK staining relate to clinical outcome.