Exome Sequencing and CNV Analysis on Chromosome 18 in Small Intestinal Neuroendocrine Tumors: Ruling Out a Suspect?

Driver mutations occur frequently in metastases of well-differentiated small intestine neuroendocrine tumours

AIMS

To investigate the clinicopathological significance of driver mutations in metastatic well-differentiated small intestine neuroendocrine tumours (SI-NETs).

METHODS AND RESULTS

Whole genome sequencing (WGS) of 35 metastatic SI-NETs and next-generation sequencing (NGS) of eight metastatic SI-NETs were performed. Biopsies were obtained between 2015 and 2019. Tumours were classified according to the 2019 World Health Organization classification. WGS included assessment of somatic mutations in all cancer-related driver genes, the tumour mutational burden (TMB), and microsatellite status. NGS entailed a cancer hotspot panel of 58 genes. Our cohort consisted of 21% grade 1, 60% grade 2 and 19% grade 3 SI-NETs. Driver mutations were identified in ~50% of SI-NETs. In total, 27 driver mutations were identified, of which 74% were in tumour suppressor genes (e.g. TP53, RB1, and CDKN1B) and 22% were in proto-oncogenes (e.g. KRAS, NRAS, and MET). Allelic loss of chromosome 18 (63%), complete loss of CDKN2A and CDKN1B (both 6%) and CDKN1B mutations (9%) were most common. Potential targetable genetic alterations were detected in 21% of metastasised SI-NETs. All tumours were microsatellite-stable and showed low TMBs (median 1.10; interquartile range 0.87-1.35). The Ki67 proliferation index was significantly associated with the presence of driver mutations (P = 0.015).

CONCLUSION

Driver mutations occur in 50% of metastasised SI-NETs, and their presence is associated with a high Ki67 proliferation index. The identification of targetable mutations make these patients potentially eligible for targeted therapy.

Molecular prognostic factors in small-intestinal neuroendocrine tumours

BACKGROUND

Small-intestinal neuroendocrine tumours (SI-NETs) represent a heterogeneous group of rare tumours. In recent years, basic research in SI-NETs has attempted to unravel the molecular events underlying SI-NET tumorigenesis.

AIM

We aim to provide an overview of the current literature regarding prognostic and predictive molecular factors in patients with SI-NETs.

METHOD

A PubMed search was conducted on (epi)genetic prognostic factors in SI-NETs from 2000 until 2019.

RESULTS

The search yielded 1522 articles of which 20 reviews and 35 original studies were selected for further evaluation. SI-NETs are mutationally quiet tumours with a different genetic make-up compared to pancreatic NETs. Loss of heterozygosity at chromosome 18 is the most frequent genomic aberration (44-100%) followed by mutations of CDKN1B in 8%. Prognostic analyses were performed in 16 studies, of which 8 found a significant (epi)genetic association for survival or progression. Loss of heterozygosity at chromosome 18, gains of chromosome 4, 5, 7, 14 and 20p, copy gain of the SRC gene and low expression of RASSF1A and P16 were associated with poorer survival. In comparison with genetic mutations, epigenetic alterations are significantly more common in SI-NETs and may represent more promising targets in the treatment of SI-NETs.

CONCLUSION

SI-NETs are mutationally silent tumours. No biomarkers have been identified yet that can easily be adopted into current clinical decision making. SI-NETs may represent a heterogeneous disease and larger international studies are warranted to translate molecular findings into precision oncology.

Mutational and copy number asset of primary sporadic neuroendocrine tumors of the small intestine

Small intestine neuroendocrine tumors (SI-NETs) represent the most common histotype among small intestine neoplasms, and metastatic disease is usually present at diagnosis. A retrospective series of 52 sporadic primary surgically resected SI-NETs, which were metastatic at diagnosis, was analyzed by high-coverage target sequencing (HCTS) for the mutational status of 57 genes and copy number status of 40 genes selected from recently published genome sequencing data. Seven genes were found to be recurrently mutated: CDKN1B (9.6%), APC and CDKN2C (each 7.7%), BRAF, KRAS, PIK3CA, and TP53 (each 3.8%). Copy number analysis showed frequent allelic loss of 4 genes located on chromosome 18 (BCL2, CDH19, DCC, and SMAD4) in 23/52 (44.2%) and losses on chromosomes 11 (38%) and 16 (15%). Other recurrent copy number variations were gains for genes located on chromosomes 4 (31%), 5 (27%), 14 (36%), and 20 (20%). Univariate survival analysis showed that SRC gene copy number gains were associated with a poorer prognosis (p = 0.047). Recurrent copy number variations are important events in SI-NET and SRC may represent a novel prognostic biomarker for this tumor type.