Abstract 4933: In Situ analysis of FGFR2 RNA and comparison with FGFR2 gene copy number by dual-color in situ hybridization in a large cohort of gastric cancer patients

Abstract

Abstract Gastric cancer is the 3rd most common cause of cancer-related mortality worldwide, thus new treatment options are urgently needed. In gastric cancer, over-expression of the tumor-promoting tyrosine kinase receptor fibroblast growth factor receptor 2 (FGFR2) has been described, representing a potential therapeutic target. FGFR2 expression in gastric cancer has been reported to be heterogeneous. Most methods for detection of RNA in FFPE (formalin fixed paraffin embedded) do not provide spatial resolution for assessment of tumor heterogeneity. Here we used a novel RNA in situ technique called RNAscope. The technology allows visual investigation of FGFR2 transcription on FFPE slides. Samples from 1036 gastric adenocarcinoma patients who underwent surgery in National Cancer Center Hospital East (Chiba, Japan) were assembled in tissue micro-arrays and analyzed by RNAscope. A total of 578 samples were also analyzed by DISH to determine gene amplification. Using these tissue based methods we were able to assess the localization and heterogeneity of both FGFR2 gene amplification and RNA expression. Strong FGFR2 gene amplification (FGFR2:CEN10 >10) was detected in 2% of 578 samples. Moderate FGFR2 gene amplification (FGFR2:CEN10 between 2 and 10) was seen in 8% of the samples. High FGFR2 RNA expression (score 4+) was seen in 4% of 718 evaluable samples. Gene amplification and RNA expression were closely correlated. All samples with dense clusters of score 4+ RNA showed FGFR2:CEN10 ratios >10. The identical tumor areas showed high gene amplification and RNA expression. FGFR2 RNA and gene amplification was highly heterogeneous in the tissue. Only 0.4% of the samples showed homogeneous FGFR2 expression in >80% of the tumor cells. High RNA expression intensity was associated with a more homogeneous expression pattern compared to moderate FGFR2 expression. In early stage I/II gastric cancer samples with score 4+ RNA expression are mostly of the differentiated type. RNA score 4+ patients of grade III/IV gastric cancer were mostly of undifferentiated histology. In a subset of 195 samples with available data cMet IHC 3+ and Her2 positivity status were not mutually exclusive with regards to FGFR2 RNA Score 4+ expression. In a multivariant analysis FGFR2 RNA expression was associated with patient outcome. Gastric cancer patients with score 4+ RNA expression had a shorter progression free survival compared to patients with score 0-3. Interestingly, there was a trend for patients with homogeneous score 3+ RNA expression, but not heterogeneous score 3+ expression, to show shorter PFS and OS suggesting that patients with high intensity or homogeneous FGFR2 RNA expression may define a subgroup of patients with gastric cancer. Patients with homogenous or strong focal FGFR2 expression might therefore be candidates for FGFR2 directed therapies in gastric cancer. Citation Format: Yasutoshi Kuboki, Christoph A. Schatz, Sabine Jabusch, Karl Koechert, Janine Feng, Sabine Wittemer-Rump, Karl Ziegelbauer, Thomas Krahn, Akiko Nagatsuma, Atsushi Ochiai. In Situ analysis of FGFR2 RNA and comparison with FGFR2 gene copy number by dual-color in situ hybridization in a large cohort of gastric cancer patients. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4933.