Experience in KRAS Mutational Analysis for Colorectal Cancer
X Liu, M Jakubowski, JL Hunt. Cleveland Clinic, Cleveland, OH
Background: Colorectal cancer (CRC) is the third leading cause of cancer-related death in the Unites States. KRAS, an oncogene, has been reported to be mutated in about 30% of CRCs. Emerging data strongly suggest that mutations in KRAS in CRCs are predictive of resistance to epidermal growth factor receptor (EGFR) inhibitor treatment. KRAS mutation analysis will be important before patients start EGFR inhibitor treatment. KRAS mutation has been suggested to be associated with poor prognosis, well to moderate differentiation, diffuse proliferation, and lack of apoptosis in CRCs. However, no detailed morphology comparison between KRAS mutation positive and wild type CRCs has been reported. This study sought to determine 1) the frequency of KRAS mutation and the most common KRAS mutation types in advanced CRCs and 2) the morphologic features associated with KRAS mutation positive CRCs.
Design: 89 cases of CRCs were included and formalin-fixed parraffin-embedded tissue sections were used for microdissection and DNA extraction. PCR was performed for a 263 basepair fragment, and the PCR product was subjected to cycle sequencing. The frequency and the types of KRAS mutations were determined. A subset of tumors were used for a detailed blinded histologic review. Features assessed included dirty necrosis, tumor differentiation, mitotic activity, apoptotic activity, mucinous component, tumor infiltrating lymphocytes, and complexity of malignant glands. The morphologic features were correlated to the KRAS mutational status. Fisher Exact test was used to analyze the data.
Results: The specimens tested included 86 primary carcinomas, and 3 metastatic CRCs. 22 specimens were found to harbor a KRAS mutation (24.7%). The mutations were distributed between codon 12 (12 cases; 54.5%) and codon 13 (10 cases; 45.57%). The types of mutation include GGT>TGT (3), GGT>GAT (6), GGT>GTT (3) in codon 12 and GGC>GAC in codon 13 (10). Histologic slides from 12 cases of KRAS mutated CRCs and 25 cases of wild type CRCs were reviewed. The histologic features that correlated with KRAS mutation were mitotic activity and apoptotic bodies (p=.045 and p=.028, respectively).
Conclusions: KRAS mutation occurs approximately in 24.7% of CRCs. The most common mutation types are GGT>GAT in codon 12 and GGC>GAC in codon 13, which accounted for 72.7% of the mutants. Tumors with mutated KRAS appears to be more mitotically active and undergo robust apoptosis.
Tuesday, March 10, 2009 11:45 AM
Platform Session: Section C, Tuesday Morning