Genomic analysis of primary malignant melanoma of the esophagus.

Abstract

e21515 Background: Primary malignant melanoma of the esophagus (PMME) is an exceedingly rare disease but behave more aggressively and have a poorer prognosis. No specific histopathological classification and therapy strategies have been established for this type of disease due to lack of both tumor biological and genetics perception to PMME. Methods: We performed whole exome sequencing on 29 dissections including 23 primary tumors and 6 metastatic lymph nodes from 18 PMME patients. The genetic characteristics including somatic mutations and copy number variation (CNV) of PMME were compared to 398 skin cutaneous melanoma (SKCM), 67 mucosal melanoma (MM) and 79 uveal melanoma (UVM). Using multi-region sequencing, we reconstructed the phylogenetic structure and inferred the evolutionary mode. Results: We found that PMME/MM have similar genomic patterns to SKCM but distinct from UVM. Frequently mutated driver genes such as MUC16, BRAF, NRAS, NF1, KMT2C, POLE, PTPRT, RANBP2 appeared in both SKCM and PMME/MM cohorts. Of note, pathway enrichment analysis using identified driver genes revealed that melanoma pathway and MAPK signaling pathway were among the top affected pathways in MM/PMME as well as in SKCM. UVR-associated single base substitution signature 7 (SBS7) was not a dominant signature (median: 0.17, range:0̃0.79) in PMME/MM but 99 percent (89/90) of them do have it. An overall concordant trend in genome instability was found between PMME and SKCM. Significant CNV events at arm level showed the similar changes in PMME and SKCM, including amplification regions of 1q, 6p, 7p, 8q, 15q, 20p and deletion of 10p, 10q, 11p. CDKN2A loss appeared as a shared focal event by PMME and SKCM. To elucidate the evolution trajectory of spatially separated samples, we also performed multi-region sequencing, and the phylogenetic analysis suggested that whole genome doubling (WGD) was an early and clonal event, which preceded the majority of somatic mutations and CNV. Most driver genes such as NF1, RANBP2 and MUC16 mutated after WGD except TP53. Above findings suggested that WGD might be capable of promoting ongoing genome instability and shaping the evolution in PMME. Moreover, parallel evolution of RANBP2 was recurrently observed indicating the existence of constraints and selection. Conclusions: Our data showed that PMME/MM exhibited genetic features very similar to SKCM so it might not be excluded from treatments currently used for common SKCM.