Intratumoral Heterogeneity of KRAS Mutations in Colorectal Carcinoma: It Is Important To Submit Which Tumor Tissue Sample for Mutation Analysis
H Baloglu, Z Kucukodaci, N Yigit, I Yilmaz, A Haholu, HA Simsek. GATA-HEH, Istanbul, Turkey; MSKCC, New York
Background: The epidermal growth factor receptor (EGFR) plays an important role in tumorigenesis and tumor progression of colorectal cancer. As a result, the EGFR has evolved as a relevant target in the treatment of metastatic colorectal cancer. KRAS serves as a mediator between extracellular ligand binding and intracellular transduction of signals from the EGFR to the nucleus. The presence of activating KRAS mutations has been identified as a potent predictor of resistance to EGFR-directed antibodies such as cetuximab or panitumumab. These agents should therefore be applied only in tumors with a wild-type status of the KRAS gene. Therefore, it is important to elucidate which patients are most likely to benefit from specific targeted therapies. The mutation analysis of only one small area from a FFPE tumor tissue could not be representative of the whole tumor because of the possibility of the heterogeneity for the occurrence of KRAS mutation. So it is an important consideration to choose the tumor sample for mutation analysis.
Design: The study population consisted of 28 patients who were treated surgically for colorectal adenocarcinoma at GATA Haydarpasa Teaching Hospital. Selective laser microdissection were performed to all paraffin blocks with tumor (total block number: 3-6, average block number: 5) and extracted DNA was amplified by the polymerase chain reaction (PCR). The PCR products were sequenced with the ABI3100 sequence analyzer (Applied Biosystems, Foster City, CA). The mutation of the KRAS gene was detected in 12 of 28 cases. Then to detect tumor heterogeneity for KRAS mutation among these 12 cases, DNA extracted with and without selective laser microdissection from each paraffin block of the tumir and independent PCR-sequencing reactions were performed. The histology of the same tumor in different blocks was not significantly different.
Results: Mutations identical to those found from all paraffin blocks with selective laser microdissection were confirmed in average of 2.8 blocks with selective laser microdissection and in average of 0.9 blocks without selective laser microdissection.
Conclusions: This study revealed that KRAS gene mutation were significantly heterogeneous in colorectal adenocarcinomas parafin blocks and indicate that it is important to select the paraffin block and to collect enough tumor cells for mutation analysis.
Tuesday, March 23, 2010 9:30 AM
Poster Session III # 115, Tuesday Morning