Integrated clinico-molecular profiling of appendiceal adenocarcinoma reveals a unique grade-driven entity distinct from colorectal cancer

Abstract

Background: Appendiceal adenocarcinoma (AA) is an orphan disease with unique clinical attributes but often treated as colorectal cancer (CRC). Understanding key molecular differences between AA and CRC is critical.

Methods: We performed retrospective analyses of AA patients (N = 266) with tumour and/or blood next-generation sequencing (NGS) (2013-2018) with in-depth clinicopathological annotation. Overall survival (OS) was examined. For comparison, CRC cohorts annotated for sidedness, consensus molecular subtypes (CMS) and mutations (N = 3283) were used.

Results: Blood-NGS identified less RAS/GNAS mutations compared to tissue-NGS (4.2% vs. 60.9%, P < 0.0001) and showed poor concordance with tissue for well-/moderately differentiated tumours. RAS (56.2%), GNAS (28.1%) and TP53 (26.9%) were most frequent mutations. Well/moderately differentiated tumours harboured more RAS (69.2%/64.0% vs. 40.5%) and GNAS (48.7%/32.0% vs. 10.1%) while moderate/poorly differentiated tumours had more TP53 (26.0%/27.8% vs. 7.7%) mutations. Appendiceal adenocarcinoma (compared to CRC) harboured significantly fewer APC (9.1% vs. 55.4%) and TP53 (26.9% vs. 67.5%) and more GNAS mutations (28.1% vs. 2.0%) (P < 0.0001). Appendiceal adenocarcinoma mutation profile did not resemble either right-sided CRC or any of the four CMS in CRC. High grade, but no mutation, was independently predictive of survival.

Conclusion: Integrated clinico-molecular profiling of AA identified key molecular drivers distinct from CRC. Appendiceal adenocarcinoma has a predominantly grade-driven biology that trumps mutations.

Fig. 1. Study Cohorts.

Flow diagram illustrating patient selection. AA appendiceal adenocarcinoma, APP appendix, CLIA clinical laboratory improvement amendments, CMS consensus molecular subtype, CRC colorectal cancer, EMR electronic medical records, IRB institutional review board, MDACC MD Anderson Cancer Center, Houston, TX, USA, MSK Memorial Sloan Kettering, New York, NY, USA, NGS next-generation sequencing, TCGA The Cancer Genome Atlas. Note: 1. https://www.cbioportal.org/study/summary?id=msk_impact_2017. 2. Twelve patients had both tissue and blood testing. 3. https://www.cancer.gov/about-nci/organization/ccg/research/structural-genomics/tcga.

Fig. 2. Tissue and Blood Sequencing in Appendiceal Adenocarcinoma.

Comparison between blood and tissue NGS vis-à-vis number of mutations per patient (a) and proportion of cases with RAS/GNAS mutations stratified by grade (c). (b) shows impact of grade in selection of patients for blood-only and tissue-only NGS. D differentiated, Mod moderately, NGS next-generation sequencing, Poor poorly.

Fig. 3. Mutational Profile of Appendiceal Adenocarcinoma.

Frequency (%) of mutations (>3% incidence) in tumour tissue from patients with appendix cancer (a), distribution of mutation (top six most frequently mutated genes) by grade/differentiation (b), distribution of number of mutations per patient (c) and distribution of number of mutations per patient by grade/differentiation (d). Comparisons are shown for only significant differences (P < 0.05). D differentiated, Mod moderately, Poor poorly.

Fig. 4. Survival Analyses of Key Prognostic Factors.

Kaplan−Meier overall survival (OS) curves for all patients by grade (a), and comparison between grade and GNAS status (b), grade and TP53 status (c), cytoreductive surgery and HIPEC (d), cytoreductive surgery and HIPEC and GNAS status (e), cytoreductive surgery and HIPEC and TP53 status (f). Only statistically significant comparisons are shown. CRS + H cytoreductive surgery and HIPEC, D differentiated, Mod moderately, MUT mutant, ND not defined, Poor poorly, WT wild type.

Fig. 5. Mutations in Appendiceal Adenocarcinoma vs. Colorectal Cancer.

Comparison (frequency %) of mutations among appendix cancer (AA) and colorectal cancer (CCR) w.r.t. sidedness (a) and consensus molecular subtypes (CMS) (b).