Study On Activation Of The Igf-1r Mtor Pathway In Neuroendocrine Tumours (Nets)

4139 Background: NETs are a heterogeneous group of rare neoplasms. Preclinical studies have shown that IGFR overestimulation can lead to constitutional activation of mTOR pathway. The main objective of this study is to describe the activation status of IGF1R-mTOR pathway by immunohistochemistry in a series of NETs and to assess the association with IGF1R expression. Methods: We studied 69 paraffin tumour blocks: 28 pancreatic NETs (pNETs) (2 gastrinomas, 1 glucagonoma, 4 insulinomas and 21 non-functioning (nf) pNETs), 32 GI NETs (4 stomach, 8 colorectum, 18 ileum and 2 dudodenum) and 9 NETs from other origins (2 anterior mediastinum, 2 ovary, 3 bile duct and 2 kidney). The expression of IGF1R, phosphorylated (p) mTOR and (p)S6 has been determined by immunohistochemistry using anti-IGF1Rβ (sc-713), anti-Phospho-mTOR (S2448) (49F9, Cell Signaling) and anti-Phospho-S6 Ribosomal Protein (S235/336)(91B2, Cell Signaling). Results: Expression of IGF1R has been observed in 46 of 69 (66%) samples with the highest expression in 2/4 (50%) insulinomas, 5/21 nf pNETs (23%) and 3/18 ileum (17%). We have observed activation of the mTOR pathway by immunodetection of (p)mTOR in 14 of 69 samples (20%): 2/21 nf pNETs (9.5%), 1/8 colorectum (12.5%), 8/18 ileum (44%), 1/2 anterior mediastinum, 1/2 ovary, 1/3 biliar tract. We haven’t detected any (p)S6 activation in these samples. Consistent IGF1R-mTOR pathway activation was detected in 11/14 (78%) samples with mTOR positivity that also showed expression of IGF1R. The most relevant finding is that all of the 8 samples from ileum with activation of mTOR showed some degree of expression of IGF1R. Conclusions: 2/3 of NETs show varying levels of expression of IGF1R, but only 16% demonstrate activation of the IGF1R-mTOR pathway. While the positivity of (p)mTOR in pNETs is lower than expected, we have identified a subgroup of ileal NETs with consistent activation of both IGF1R and (p)mTOR which could help stratify patients in clinical trials involving modulation of this pathway. In contrast, none of the 69 samples studied was positive for (p)S6 which suggests this marker is not valid to be used in the clinic. Further validation studies are required to help clinical stratification for therapies against IGF1R mTOR pathways.