Gene expression profiles depend on tumor locations in

Colorectal Cancer (left vs. right vs. rectum)

BACKGROUND

Recent data suggests that CRC from different locations show distinct genetic profiles. Right-sided tumors have a worse prognosis and may have less benefit from targeted therapies. We investigated the tumor locations and genetic profiles (KRAS and BRAF mutation status and ERCC1, TS, EGFR and VEGFR2 mRNA expression) in 580 CRC tumors.

M.K.H. Maus1,2, D.L. Hanna4, C. Stephens2, P. P. Grimminger1, M. Epstein1, S.H. Astrow2, D. Yang4, F. Loupakis4,5, J. Hsiang1, G. Zeger2,3, T. Wakatsuki4, A. Barzi4, H.J. Lenz4

1 Department of General, Visceral, and Tumor Surgery, University of Cologne, GERMANY; 2 Response Genetics, Inc., Los Angeles, CA, USA; 3 Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, USA; 4 Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, USA; 5 Oncologia Medica, Azienda Ospedaliero-Universitaria Pisana, Instituto Toscano Tumori, Pisa, ITALY

METHODOLOGY

FFPE tumor specimen from 580 patients with advanced CRC adenocarcinoma were microdissected and DNA and RNA were extracted. Specifically designed primers and probes were used to detect 7 different base substitutions in codon 12 and 13 of KRAS, V600E mutations in BRAF and the mRNA expression levels of ERCC1, TS, EGFR and VEGFR2 by RT-PCR. These values were analyzed according to tumor location (left vs. right vs. rectum).

RESULTS

BRAF mutations were significantly more common in the right colon (15%), followed by rectum (3.8%) and left colon (2.5%). KRAS mutations occurred at similar frequencies throughout the colon. Gene expression of ERCC1 was significantly higher in right-sided than left-sided colon tumors in KRAS wild-type colon cancers. The highest expression levels for all genes were seen in rectum. These differences reached significant levels for ERCC1 (rectum vs. right and rectum vs. left, p<0.001), TS (rectum vs. left, p<0.036) and VEGFR2 (rectum vs. right and rectum vs. left, p<0.001).

CONCLUSION

Tumor location in CRC is associated with specific mutation and expression profiles. Differences in chemosensitivity may be explained by mutation status and mRNA levels in right vs. left CRC. Rectum cancers showed a distinct genetic profile when compared to colon which indicates a different tumor biology. The genetic differences between right and left colon and rectum may be used in making treatment decisions in the future.

Right Colon Left Colon Rectum

14.8%

2.5% 3.8%

44%

41%44%

BRAF MT KRAS MT

Frequency of BRAF and KRAS mutations in right and left colon and rectum Right Left Rectum

Gene KRAS N Median (range) N Median (range) N Median (range)

ERCC1 Mutant 77 0.82 (0.26 - 2.95) 66 0.82 (0.27 - 2.96) 32 0.96 (0.23 - 2.60)

Wildtype 78 0.98 (0.28 - 3.06) 86 0.84 (0.17 - 6.66) 46 1.25 (0.37 - 4.23)

P value* 0.005 0.77 0.052

All 161 0.91 (0.26 - 3.06) 161 0.83 (0.17 - 6.66) 88 1.11 (0.23 - 4.23)

Pairwise‡ ×, ×, P value† <0.001

 

TS2 Mutant 76 1.90 (0.52 - 9.43) 66 1.92 (0.81 - 9.26) 31 2.69 (0.77 - 21.43)

Wildtype 78 2.42 (0.65 - 13.81) 84 2.25 (0.65 - 10.02) 46 2.66 (0.97 - 18.99)

P value* 0.019 0.27 0.80

All 160 2.19 (0.52 - 13.81) 159 2.10 (0.65 - 10.26) 85 2.60 (0.77 - 21.43)

Pairwise‡ × ×

P value† 0.036

 

EGFR Mutant 76 1.60 (0.33 – 7.17) 66 1.61 (0.79 – 5.24) 32 1.66 (0.78 – 4.08)

Wildtype 75 2.12 (0.63 – 7.45) 88 1.78 (0.63 – 5.68) 44 2.20 (0.80 – 71.28)

P value* 0.001 0.12 0.11

All 160 1.88 (0.33 - 7.45) 163 1.71 (0.60 - 5.68) 83 1.92 (0.75 - 71.28)

Pairwise‡

P value† 0.19

VEGFR2 Mutant 50 0.91 (0.24 – 6.10) 41 1.33 (0.25 – 7.66) 25 1.53 (0.23 – 3.62)

Wildtype 54 1.29 (0.33 – 5.94) 66 1.21 (0.18 – 6.64) 38 2.21 (0.37 – 13.00)

P value* 0.014 0.69 0.016

All 108 1.10 (0.24 - 6.10) 110 1.24 (0.18 - 7.66) 68 1.77 (0.23 - 13.00)

Pairwise‡ × ×, P value† <0.001

Gene expression levels by tumor site and KRAS mutation status

*Based on Wilcoxon two - sample test for differences by KRAS mutation status in each tumor site.† Based on Kruskal-Wallis test for differences across tumor sites.‡ Based on Wilcoxon two - sample test for pairwise differences by two tumor sites adjusting for multiple comparisons. The same symbol represents a significant pairwise difference.