DNA mutation frequencies in metastatic small bowel adenocarcinoma (mSBA) in comparison to gastric (mGC), colon (mCC), and rectal cancer (mRC): Continuum or cutpoint?

Abstract

e14636 Background: The small intestine is in continuity with the stomach and colon/rectum. However mGC and mCC/mRC differ in oncogene profiles. No study has evaluated the oncogene profile of mSBA on the continuum of mGC and mCC/mRC. This may give insight into biology and have implications for treatment. Methods: Respective analysis was performed on GI cancer patients who underwent tumor mutational profiling since 2010. Genotyping was performed on formalin-fixed and paraffin-embedded tumor tissue using a multiplexed mutational profiling platform. Here we report results for APC, BRAF, EGFR, IDH1, KRAS, NRAS, PI3K, PTEN, and TP53. Results: We identified 12 patients with mSBA (11/12 with clinical data, 11/12 with genotype data). Median age at stage IV diagnosis was 61.1y (49.3-71.5y). Four patients had duodenal, 3 jejeunal, 2 ileal, and 2 multiple/unknown primary sites. All patients received 5FU and ox, while 8/11 received irino, 5/11 bev, 3/11 cetux, 1/11 regorafenib and 1/11 capecitabine. Two patients had adjuvant RT (both duodenal) while 4/11 received palliative RT. Survival was calculated from the date of stage IV diagnosis until death, with data censored on 2/1/2013. Median survival was 24.0 months (95% CI 6.4 – 60.0 mo). We compared genotype frequencies of mSBA patients (11) with mGC (41), mCC (161), and mRC (64) using Fisher’s exact test for pairwise comparisons. Conclusions: While the small bowel sample size was small, a significant difference in KRAS mutation frequency was found when compared to gastric cancer. No significant differences in mutation frequencies were found when compared with colon or rectal cancer. [Table: see text]