EGFR fluorescence in situ hybridization pattern of chromosome 7 disomy predicts resistance to cetuximab in KRAS wild-type metastatic colorectal cancer patients.

Purpose: Metastatic colorectal cancer patients with low epidermal growth factor receptor (EGFR) gene copy number are unlikely to respond to anti-EGFR monoclonal antibody (mAb) treatment. The objective of this study was to investigate EGFR fluorescence in situ hybridization (FISH) patterns of chromosome 7 disomy with efficacy of cetuximab therapy in metastatic colorectal cancer patients.

Experimental Design: We detected the EGFR FISH patterns and KRAS status in 74 tumors from cetuximab-treated metastatic colorectal cancer patients and analyzed with response rate (RR) and progression-free survival (PFS).

Results: One of the 16 (6.25%) patients with chromosome 7 homogeneous disomy (defined as FISH negative) had objective response to cetuximab. A total of 53(76.8%) patients with chromosome 7 pattern of variable ratios of disomy versus polysomy (defined as FISH positive) had a significantly higher RR (37.7% versus 6.25%; P = 0.01), a trend towards longer PFS (4.5 versus 2.9 months; P = 0.07). Among 54 KRAS wild-type patients, EGFR FISH-positive patients had significantly higher RR (51.3% versus 9%; P = 0.01) and longer PFS (5.0 versus 2.3 months; P = 0.02) than EGFR FISH-negative patients. However, among 20 KRAS mutant-type patients, there was no difference in RR (0% versus 0%) and PFS (2.5 versus 3.8 months; P = 0.51) between EGFR FISH-positive and -negative patients.

Conclusion: Our results show firstly that patients with EGFR FISH pattern of chromosome 7 disomy have a very low chance to benefit from cetuximab-based therapy. EGFR FISH pattern of chromosome 7 disomy may be as a negative predicative factor for cetuximab response in KRAS wild-type metastatic colorectal cancer patients.