Somatic alterations of NF1 in colorectal cancer.

Abstract

4066 Background: NF1 encodes neurofibromin, which is a key GTPase-activating protein that downregulates RAS activation. Inactivating mutations in NF1 result in sustained activation of RAS signaling, a key driver for development of colorectal cancer (CRC), and have been suggested to be a potential mechanism of resistance to EGFR inhibition in RAS-wild type (WT) CRC. Little is known about molecular characteristics of NF1-mutated (MT) CRC. Methods: Tumor profiles from 8150 CRC patients (pts) with available NF1 mutation status were retrospectively reviewed. NextGen sequencing by a customized 592-gene panel was performed. Microsatellite instability (MSI) / mismatch repair (MMR) status, tumor mutational burden (TMB) and PD-L1 expression were tested. Molecular profiles between NF1-MT and NF1-WT pts were compared. Results: Out of 8150 pts, 176 (2.2%) had somatic NF1 mutations with pathogenic or presumed pathogenic function. A higher NF1-MT frequency was observed in MSI-H/dMMR vs MSS/pMMR (13.5% vs 1.4%, p < 0.0001), in right-sided vs left sided (2.9% vs 1.8%, p < 0.01), and in RAS-WT vs RAS-MT (3.0% vs 1.4%, p < 0.0001). In MSS/pMMR tumors, no association with sidedness was observed (right: 1.3% vs left: 1.2%, NS). The most prevalent co-mutations with NF-1 were APC (63.2%), ARID1A (57.5%), TP53 (51.5%), KMT2D (32.9%) and KRAS (32.4%) in all cases, and APC (76.2%), TP53 (69.5%), KRAS (38.8%), ARID1A (34.4%) and FBXW7 (21.5%) in MSS/pMMR cases. POLE mutation was observed in 18.4% of NF1-MT/MSS/pMMR pts. Compared to NF1-WT pts, NF1-MT pts had more frequent mutations in ARID1A (All: 57.5% vs 23.3%, p < 0.0001; MSS/pMMR: 34.4% vs 15.2%, p < 0.05), and less frequent mutations in KRAS (All: 32.4% vs 49.0%, p < 0.0001; MSS/pMMR: 38.8% vs 50.3%, p < 0.05). Also, NF1-MT pts had more frequent alterations in homologous recombination pathway compared to NF1-WT pts (All: 39.8% vs 7.5%, p < 0.0001; MSS/pMMR: 17.5% vs 4.4%, p < 0.0001). Mean TMB was significantly greater in NF1-MT than NF1-WT (All: 48.9/Mb vs 10.0/Mb, p < 0.0001; MSS/pMMR: 48.3/Mb vs 8.2/Mb, p < 0.0001). Also, PD-L1 positivity was higher in NF1-MT compared to NF1-WT (All: 12.9% vs 3.6%, p < 0.0001; MSS/pMMR: 7.1% vs 2.6%, p < 0.05). Conclusions: While more frequent than in RAS-MT pts, NF1-MT CRC was a small subset in RAS-WT pts. NF1-MT was associated with alterations in chromatin remodeling and DNA damage response pathways, as well as elevated TMB and PD-L1 expression, which may provide alternative therapeutic strategies beyond EGFR inhibition.