Detection of Rare Variant of SS18-SSX1 Fusion Gene and Mutations of Important Cancer-Related Genes in Synovial Sarcoma of the Lip: Gene Analyses of a Case and Literature Review

J Oral Maxillofac Surg. 2015 Aug;73(8):1505-15. doi: 10.1016/j.joms.2015.02.010. Epub 2015 Mar 16.

Abstract

Synovial sarcoma (SS) accounts for 5 to 10% of soft tissue sarcomas; however, intraoral SS is rare. Histopathologically, SS shows a biphasic pattern with epithelial and spindle cell components or a monophasic pattern with only spindle cells. The precise diagnosis of SS, especially at an unusual site, is often a challenge to pathologists and clinical oncologists, because the differential diagnosis of SS includes a broad range of tumors, such as soft tissue sarcomas and carcinomas. In the present case, the patient was a 50-year-old woman who presented with the chief complaint of swelling and a slowly enlarging mass of the lower lip in the mucolabial fold region. The mass was covered with intact mucosa and intraoral examination showed no malignant findings. The clinical diagnosis was a benign tumor and a probable salivary gland tumor. Macroscopically, the excised mass also indicated a benign tumor; however, histopathologic findings suggested the diagnosis of SS. For definitive diagnosis, genetic analyses were performed with conventional polymerase chain reaction and next-generation sequencing. As a result, a rare variant of the SS18-SSX1 fusion transcript, which could not be identified by routine procedures for genetic diagnosis, was detected. In addition, 8 missense mutations of cancer-related genes were confirmed. Detection of the fusion transcript is widely used in the diagnosis of SS; however, reported cases of transcript variants of each fusion gene type are limited. Reports of mutational analysis of cancer-related genes on SS also are rare. The accumulation of rare transcript variants and the cytogenetic characters of SS are suggested to be necessary for assuming a genetic diagnosis of SS.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • DNA Primers
  • Female
  • Gene Fusion*
  • Humans
  • Lip Neoplasms / genetics*
  • Middle Aged
  • Mutation, Missense*
  • Neoplasm Proteins / genetics*
  • Proto-Oncogene Proteins / genetics*
  • Repressor Proteins / genetics*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sarcoma, Synovial / genetics*
  • Sequence Analysis, DNA

Substances

  • DNA Primers
  • Neoplasm Proteins
  • Proto-Oncogene Proteins
  • Repressor Proteins
  • SS18 protein, human
  • synovial sarcoma X breakpoint proteins