[1639] EGFR Mutation Is a Better Predictor of Response to TKIs in NSCLC Than FISH, CISH, or IHC

LM Sholl, V Joshi, D Jackman, Y Xiao, C Lee, P Janne, N Lindeman. Brigham and Women's Hospital, Boston, MA; Harvard University, Boston, MA; Dana Farber Cancer Institute, Boston, MA

Background: 10% of patients with advanced NSCLC respond to epidermal growth factor receptor (EGFR)-targeted tyrosine kinase inhibitor (TKI) therapy. >75% of the tumors that respond have activating mutations in the EGFR gene. However, mutation analysis is not widely available, and proposed alternative assays, such as FISH or CISH for EGFR copy number (CN), and immunohistochemistry (IHC) for protein expression have shown inconsistent associations with TKI therapy response.
Design: EGFR mutation, CN, and protein expression were studied in 43 NSCLC samples from patients treated with TKIs with known treatment response (per RECIST criteria). Stable nonprogression was included with partial response as a favorable outcome. DNA was extracted from unstained 5-um paraffin sections containing >50% tumor cells; EGFR mutations were detected by PCR-capillary sequencing. FISH, CISH and IHC assays were performed on a tissue microarray containing 5 cores from each sample. Modal EGFR copy numbers seen by CISH were categorized as either disomic (2 signals), low polysomy (<5), high polysomy (HP)(5-7), or amplified (8+ or homogenous staining regions). FISH was scored by the method of Varella-Garcia, et al. HP/amplified cases were considered CN positive. Modal membranous IHC intensity (0-4) was multiplied by % of cells staining to give an index from 0-400; scores 100 were considered positive.
Results: 24/43 (56%) patients had a favorable outcome after TKI treatment. Favorable outcomes were observed in 16/20 (80%) patients with mutations vs. 8/23 (35%) WT patients (p = 0.005); in 9/16 (54%) patients with high CN vs. 13/24 (56%) CN negative cases (p=1); and in 7/9 (78%) of IHC positive cases vs. 12/25 (48%) IHC negative cases (p=0.24). Moreover, neither IHC nor CN were associated with mutation: 9/17 (53%) IHC positive cases were mutated vs. 10/21 (48%) IHC negative cases, and 10/16 (63%) CN positive cases were mutated vs. 8/24 (33%) CN negative cases (p=0.10). There was a trend toward higher copy number in IHC positive cases (p=0.04).
Conclusions: EGFR sequence, copy number, and/or protein expression can all be altered in NSCLC. However, only mutation predicts response to TKI therapy. Increased EGFR copy number, but not mutation, correlates with protein overexpression.
Category: Pulmonary

Monday, March 9, 2009 8:30 AM

Platform Session: Section F, Monday Morning