[607] Phosphorylation of EGFR in Colorectal Cancer

Jacob R Bledsoe, Daniel E Shvetz, Mari Mino-Kenudson. Massachusetts General Hospital, Boston, MA

Background: Dysregulated signaling through the MAP-Kinase (MAPK) pathway has been implicated in colorectal cancer (CRC) and occurs in the setting of mutations resulting in constitutive activation of pathway intermediates such as KRAS and BRAF. In CRC the BRAF mutation is associated with a worse prognosis and decreased response to EGFR inhibitors. BRAF-mutated CRC also shows a poor response to BRAF inhibitors in comparison to BRAF-mutated melanoma. Recent studies have shown that activation of EGFR may result in maintenance of MAPK signaling in BRAF-mutated CRC in the presence of BRAF inhibitors, thereby resulting in diminished efficacy of the inhibitor. However, the activation status of EGFR in CRC before treatment with BRAF inhibitors is not known.
Design: The study cohort consisted of 122 CRC cases. As part of the clinical workup, all cases had undergone analysis of driver mutations using a multiplex PCR assay. Of those, 22 cases harbored BRAF V600E mutations, none of which had been treated with a BRAF inhibitor prior to sample acquisition. Immunohistochemistry for EGFR, its activated form p-EGFR, and the activated MAPK effector p-ERK was performed on tissue microarrays and tumor sections. Average composite scores for staining were assigned using the H-score (maximum score 300) for each case. For each antibody, the cut-off for positive expression was determined based on the expression seen in normal colonic epithelium. P-EGFR expression was correlated with EGFR and p-ERK expression, driver mutation, and clinical parameters including clinical stage and prognosis.
Results: Positive expression of p-EGFR was seen in 7.6% of the examined cases, that of EGFR in 26%, and that of p-ERK in 26%. The expression level of p-EGFR was correlated with EGFR (p<0.0001) and p-ERK (p=0.0112) expression in the tumor samples. Positive p-EGFR expression was seen in one case with a BRAF mutation, 3 cases with TP53 mutations, and 5 cases without any mutations. EGFR and p-EGFR expression was not significantly associated with specific mutations, including BRAF and KRAS mutations. Increased MAPK activation, as determined by p-ERK over-expression, was seen in cases with KRAS (p=0.0079), but not BRAF mutations. There was no difference in the clinical parameters and prognosis between cases with and without positive p-EGFR expression.
Conclusions: Activation of EGFR is not frequent in “BRAF inhibitor-naive” CRC although it can be seen in rare BRAF mutated tumors, and is associated with activation of downstream target, ERK. Further studies are warranted in order to elucidate post-treatment changes in EGFR activation in BRAF-mutated CRC treated with BRAF inhibitors.
Category: Gastrointestinal

Monday, March 4, 2013 1:00 PM

Poster Session II # 137, Monday Afternoon


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