[726] KRAS Mutational Testing in Tumor Samples Obtained before and after Chemoradiation in Rectal Cancer Patients: Different Protocols on the Basis of Available Tissues.

Elena Zanellato, Francesca Molinari, Martina Nucifora, Stefano Crippa, Alessandra Franzetti-Pellanda, Piercarlo Saletti, Massimo Bongiovanni, Luca Mazzucchelli, Milo Frattini. Institute of Pathology, Locarno, Switzerland; Oncology Institute of Southern Switzerland, Bellinzona, Switzerland

Background: KRAS testing represents the prerequisite for administration of EGFR-targeted therapies to metastatic colorectal cancer patients. The choice of tumor blocks for KRAS testing is fundamental. In patients with locally advanced rectal cancer (LARC), chemoradiation is generally offered before curative surgery, therefore only small tumor amounts are available at diagnosis.
Design: We tested the KRAS mutational status (using two methods) on biopsies and tumor blocks obtained before and after chemoradiation to evaluate whether differences occurred between the two materials, and the two methods. Tumors samples obtained before (diagnostic biopsy) and post (surgery specimen) neoadjuvant chemoradiation from 61 LARC patients were analyzed. Tumor microdissection was performed. KRAS status was evaluated by direct sequencing (DS, sensitivity of 10-20%) and by mutant-enriched PCR (ME-PCR, sensitivity of 0.01%).
Results: In pretreated biopsies, DS revealed KRAS mutations in 24 cases, ME-PCR in 28. In post-treated tumors, DS found KRAS mutations in 13 cases and ME-PCR in 24. Eight cases showed a discordant pattern between pre and post-therapy tissues: six patients showed the KRAS mutation limited to the pre-treated biopsy (in 4 cases detected by DS and ME-PCR, in 2 cases only by ME-PCR), two patients showed the mutation limited to the post-treated tissue (detected only by ME-PCR).
Conclusions: The use of ME-PCR enhances the detection of KRAS mutations in LARC. Discrepancies between pre- and post-chemoradiation tissues may occur. If the pre-treatment biopsies are available, DS can be routinely used. Although carefully microdissected, post-chemoradiation biopsies must be evaluated only by high sensitive methodologies, such as ME-PCR.
Category: Gastrointestinal

Wednesday, March 2, 2011 9:30 AM

Poster Session V # 58, Wednesday Morning


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