Discovery and validation of an ancillary genomic test of malignancy for primary melanocytic tumors

Background:Pathological diagnosis of melanocytic tumors can be difficult and prone to error. More accurate and reliable ancillary investigations than those currently available are required to improve diagnostic accuracy. Goals: (1) to generate a genomic model for distinguishing benign (nevi) from malignant (melanoma) melanocytic skin tumors, developed from a customized gene panel evaluated on a cohort of 250 nevi and melanomas. (2) To evaluate the performance of the genomic model in melanocytic tumors of uncertain diagnosis/behavior. Details: The cohort of 250 melanomas and naevi was split into a discovery set and a validation set. Our genomic model obtained an area under the curve of 95% in the discovery cohort and 96% for the validation cohort. Based on a Youden index threshold, the resulting classifier shows high specificity (>95% in the discovery and validation cohorts), with sensitivities >80% in the discovery and validation cohorts. Evaluation of the genomic model on a cohort of 110 melanocytic tumors identifies key driver mutations in agreement with the likely pathway of origin of the tumors. The probability of melanoma (p=0.02) from the genomic model was significantly associated with pathology-based estimates of malignancy for melanocytic tumors lacking pathway-defining genomic aberrations (conventional tumors). The genomic model identified 8/36 (22%) conventional tumors with unresolved malignancy to have a high probability of melanoma, with 7/8 of these cases showing negative/non-aberrant results with either fluorescent in-situ hybridization, PRAME and/or p16 immunostains. Furthermore, no evidence of malignant behavior based on the genomic model was seen in 4 conventional borderline tumors with more than 1 year follow-up. Conclusion: This genomic model can become a clinically useful ancillary tool that is highly specific for differentiating melanomas from nevi.

Type: Cancer Genomics
Archiver: European Genome-Phenome Archive (EGA)

1 Dataset

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Dataset ID	Description	Technology	Samples
EGAD50000001297	This dataset was derived from 360 formalin-fixed paraffin-embedded (FFPE) samples distributed across (i) 118 primary melanomas, (ii) 132 nevi and (iii) 110 melanocytic tumors. Next generation sequencing (NGS) libraries were prepared following the FFPE DNA Archer VariantPlex Somatic Protocol for Illumina. Input DNA was determined by the PreSeq DNA QC assay, with 100 ng of DNA used for samples with high quality scores, 200 ng for low quality scores and 300 ng for samples with bad quality scores as defined by the PreSeq DNA QC assay. NGS libraries were quantified using the KAPA Library Quantification Kit for Illumina (KK4824) and sequencing performed on the Nextseq 500/2000 without custom primers using paired-end sequencing (151bp for Read 1 and Read 2) with index reads (8bp for Index Read 1 and Index Read 2). For each sample, resulting paired-end fastq files are available as part of this dataset. Prefix for each sample name is associated with the the type of sample: NAE: nevi samples. MEL: Melanoma samples. BL: melanocytic tumor.	unspecified	360