Purpose: Tumor screening for Lynch syndrome is recommended in all or most patients with colorectal cancer (CRC). In metastatic CRC, sequencing of RAS/BRAF is necessary to guide clinical management. We hypothesized that a next-generation sequencing (NGS) panel that identifies RAS/BRAF and other actionable mutations could also reliably identify tumors with DNA mismatch repair protein deficiency (MMR-D) on the basis of increased mutational load. Methods: We identified all CRCs that underwent genomic mutation profiling with a custom NGS assay (MSK-IMPACT) between March 2014 and July 2015. Tumor mutational load, with exclusion of copy number changes, was determined for each case and compared with MMR status as determined by routine immunohistochemistry. Results: Tumors from 224 patients with unique CRC analyzed for MMR status also underwent MSK-IMPACT. Thirteen percent (n = 28) exhibited MMR-D by immunohistochemistry. Using the 341-gene assay, 100% of the 193 tumors with < 20 mutations were MMR-proficient. Of 31 tumors with ≥ 20 mutations, 28 (90%) were MMR-D. The three remaining tumors were easily identified as being distinct from the MMR-D tumors with > 150 mutations each. Each of these tumors harbored the P286R hotspot POLE mutation consistent with the ultramutator phenotype. Among MMR-D tumors, the median number of mutations was 50 (range, 20 to 90) compared with six (range, 0 to 17) in MMR-proficient/POLE wild-type tumors (P < .001). With a mutational load cutoff of ≥ 20 and < 150 for MMR-D detection, sensitivity and specificity were both 1.0 (95% CI, 0.93 to 1.0). Conclusion: A cutoff for mutational load can be identified via multigene NGS tumor profiling, which provides a highly accurate means of screening for MMR-D in the same assay that is used for tumor genotyping.

Purpose: Even if RAS-BRAF wild-type and HER2/MET–negative metastatic colorectal cancer (mCRC) patients frequently respond to anti-EGFR mAbs, acquired resistance almost invariably occurs. Mechanisms of resistance to EGFR blockade include the emergence of KRAS, NRAS, and EGFR extracellular domain mutations as well as HER2/MET alterations. However, these findings derive from retrospective studies that analyzed one single resistance mechanism at a time; moreover, it is still unclear how molecular heterogeneity affects clonal evolution in patients. In this work, we aimed at extensively characterizing and correlating the molecular characteristics of tissue- and blood-based data in a prospective cohort of patients with mCRC who received anti-EGFR antibodies. Experimental design: Twenty-two RAS-BRAF wild-type, HER2/MET–negative mCRC patients progressing on anti-EGFR therapy after initial response underwent rebiopsy. Next-generation sequencing and silver in situ hybridization (SISH)/IHC analyses were performed both on archival tumors and postprogression samples. Circulating tumor (ctDNA) molecular profiles were obtained in matched tissue–plasma samples. Results: RAS mutations and HER2/MET amplification were the most frequently detected resistance mechanisms in both tissue and blood sample analysis. On the other hand, BRAF and EGFR ectodomain mutations were much rarer. Patients with acquired MET amplification showed worse PFS on anti-EGFRs. We detected both intralesion heterogeneity, as suggested by co-occurrence of different resistance mechanisms in the same sample, and interlesion heterogeneity. The combined analysis of tissue and blood (ctDNA) results highlights the complexity of clonal evolution triggered by EGFR blockade. Conclusions: Our results indicate that it may be extremely challenging to target the complex landscape of molecular heterogeneity associated with emergence of resistance to targeted therapies in patients with mCRC. Clin Cancer Res; 23(10); 2414–22. ©2016 AACR.

Purpose: GEP-NENs are rare malignancies with increasing incidence. Their molecular characteristics are still undefined. We explored the underlying biology of GEP-NENs and the differences between gastrointestinal (GI) and pancreatic (PNEN), high-grade (HG), and low-grade (LG) tumors.Experimental Design: GEP-NENs were analyzed using next-generation sequencing (NGS; MiSeq on 47 genes, NextSeq on 592 genes), IHC, and in situ hybridization. Tumor mutational burden (TMB) was calculated on the basis of somatic nonsynonymous missense mutations, and microsatellite instability (MSI) was evaluated by NGS of known MSI loci.Results: In total, 724 GEP-NENs were examined: GI (N = 469), PNEN (N = 255), HG (N = 135), and LG (N = 335). Forty-nine percent were female, and median age was 59. Among LG tumors, the most frequently mutated genes were ATRX (13%), ARID1A (10%), and MEN1 (10%). HG tumors showed TP53 (51%), KRAS (30%), APC (27%), and ARID1A (23%). Immune-related biomarkers yielded a lower prevalence in LG tumors compared with HG [MSI-H 0% vs. 4% (P = 0.04), PD-L1 overexpression 1% vs. 6% (P = 0.03), TMB-high 1% vs. 7% (P = 0.05)]. Compared with LG, HG NENs showed a higher mutation rate in BRAF (5.4% vs. 0%, P < 0.0001), KRAS (29.4% vs. 2.6%, P < 0.0001), and PI3KCA (7% vs. 0.3%, P < 0.0001). When compared with GI, PNEN carried higher frequency of MEN1 (25.9% vs. 0.0%, P < 0.0001), FOXO3 (8.6% vs. 0.8%, P = 0.005), ATRX (20.6% vs. 2.0%, P = 0.007), and TSC2 (6.3% vs. 0.0%, P = 0.007), but lower frequency of mutations in APC (1.0% vs. 13.8%, P < 0.0001).Conclusions: Significant molecular differences were observed in GEP-NENs by tumor location and grade, indicating differences in carcinogenic pathways and biology.