RESUMO
BACKGROUND: Genome-wide profiling of rare tumors is crucial for improvement of diagnosis, treatment, and, consequently, achieving better outcomes. Desmoplastic small round cell tumor (DSRCT) is a rare type of sarcoma arising from mesenchymal cells of abdominal peritoneum that usually develops in male adolescents and young adults. A specific translocation, t(11;22)(p13;q12), resulting in EWS and WT1 gene fusion is the only recurrent molecular hallmark and no other genetic factor has been associated to this aggressive tumor. Here, we present a comprehensive genomic profiling of one DSRCT affecting a 26-year-old male, who achieved an excellent outcome. METHODS: We investigated somatic and germline variants through whole-exome sequencing using a family based approach and, by array CGH, we explored the occurrence of genomic imbalances. Additionally, we performed mate-paired whole-genome sequencing for defining the specific breakpoint of the EWS-WT1 translocation, allowing us to develop a personalized tumor marker for monitoring the patient by liquid biopsy. RESULTS: We identified genetic variants leading to protein alterations including 12 somatic and 14 germline events (11 germline compound heterozygous mutations and 3 rare homozygous polymorphisms) affecting genes predominantly involved in mesenchymal cell differentiation pathways. Regarding copy number alterations (CNA) few events were detected, mainly restricted to gains in chromosomes 5 and 18 and losses at 11p, 13q, and 22q. The deletions at 11p and 22q indicated the presence of the classic translocation, t(11;22)(p13;q12). In addition, the mapping of the specific genomic breakpoint of the EWS-WT1 gene fusion allowed the design of a personalized biomarker for assessing circulating tumor DNA (ctDNA) in plasma during patient follow-up. This biomarker has been used in four post-treatment blood samples, 3 years after surgery, and no trace of EWS-WT1 gene fusion was detected, in accordance with imaging tests showing no evidence of disease and with the good general health status of the patient. CONCLUSIONS: Overall, our findings revealed genes with potential to be associated with risk assessment and tumorigenesis of this rare type of sarcoma. Additionally, we established a liquid biopsy approach for monitoring patient follow-up based on genomic information that can be similarly adopted for patients diagnosed with a rare tumor.
Assuntos
Neoplasias Abdominais/diagnóstico por imagem , Tumor Desmoplásico de Pequenas Células Redondas/diagnóstico por imagem , Neoplasias Abdominais/genética , Neoplasias Abdominais/terapia , Adulto , Biomarcadores Tumorais/sangue , Biomarcadores Tumorais/genética , Cromossomos Humanos Par 11/genética , DNA de Neoplasias/sangue , DNA de Neoplasias/genética , Tumor Desmoplásico de Pequenas Células Redondas/genética , Tumor Desmoplásico de Pequenas Células Redondas/terapia , Humanos , Masculino , Técnicas de Diagnóstico Molecular , Polimorfismo Genético , Translocação GenéticaRESUMO
Pediatric tumors are heterogenous and can be quite varied in appearance. However, those in the infamous "small round blue-cell tumor" group, with their hyperchromatic nuclei and small amount of cytoplasm can be challenging, and their diagnosis and prognostication require cost-efficient and focused immunohistochemistry and ancillary testing. Ideally, ample material should be obtained for routine histology and ancillary testing, including immunohistochemistry, fluorescent in situ hybridization, fresh tissue for cytogenetic studies, and snap-frozen tumor for DNA/RNA extraction both for routine molecular testing (ie, reverse-transcription PCR studies), as well as future research study protocols (genome wide studies, targeted gene sequencing). This review focuses on the main pediatric tumors with emphasis on immunophenotype, keeping in mind that a directed panel approach yields the highest yield with combination of clinical history, histologic features, and ancillary molecular testing.