Molecular Diagnosis of Retinoblastoma Cancer: A Review

Retinoblastoma (RB) is the most common primary intraocular tumor in children, which is caused by mutations in both alleles of the RB۱ tumor suppressor gene. Its mortality rate is approximately ۳.۷ cases per million and some patients suffer from strabismus and blindness. In addition, ۲۵% of patients with bilateral RB are at risk for trilateral retinoblastoma, a similar brain tumor. As a result, delay in diagnosis can lead to a high risk of metastasis and poorer outcomes. Currently used diagnostic methods are indirect ophthalmoscopy, ocular ultrasonography (B-scan), and magnetic resonance imaging (MRI), which may not be efficient for early detection and diagnosis of hereditary RB. Therefore, we reviewed and summarized the novel molecular diagnostic methods of RB. Methods: Multiple databases, including PubMed, Science Direct, Google Scholar, Scopus, etc., were searched using the terms "retinoblastoma" and "molecular diagnosis". The search was limited to reviews, case reports, and observational studies published since ۲۰۲۰. Duplicate and irrelevant articles were excluded. Results: Recently, due to the lack of specific metabolic biomarkers, there has been an increase in novel approaches for early detection and diagnosis of RB. Microarray analysis of extracted microRNAs (miRNA), including miR-۳۷۳, miR-۴۹۴, and miR-۱۹۸, were upregulated in RB samples and were reported to be efficient for the early detection of RB. Circulating miRNAs such as miR-۳۲۰, miR-۲۱, and let-۷e, as non-invasive biomarkers, correlate with RB progression and can be extracted and analyzed from various body fluids. Amplification of ۱q, ۲p, ۶p, and loss of ۱۳q and ۱۶q۱۴ were identified by Karyotyping and comparative genomic hybridization (CGH). Increases in the oncogene kinesin family member ۱۴ (KIF۱۴) were also observed, followed by increases in MYCN (N-myc proto-oncogene protein) and E۲F transcription factor ۳ (E۲F۳). Proteomic profiling biomarkers in RB tissues, including cellular retinoic acid binding protein ۲ (CRABP۲), peroxiredoxin ۶, apolipoprotein A۱, and recoverin, were significantly upregulated in invasive RB. Cell-free DNA (cfDNA) isolated from both plasma and aqueous humor (AH), including genomic DNA fragments and circulating tumor DNA (ctDNA), may predict RB prognosis by using AH cfDNA methylation profiling, which shows hypermethylation of the RB۱ promoter. Some biomarkers have emerged from AH liquid biopsy analysis, including ۶p chromosomal and/or MYCN amplification. The use of next-generation sequencing (NGS) based on RB۱ gene target enrichment has also demonstrated the ability to detect ctDNA in patients and can identify RB۱ gene variants with a diagnostic rate of ۸۵%. Moreover, the cfDNA approach can be used for prenatal screening with DNA extracted from amniotic fluid. Conclusion: Retinoblastoma accounts for ۳% of all childhood cancers, affecting ۹۰۰۰ children annually. In recent years, significant progress has been made in understanding the molecular biology of the tumor and in molecular diagnostic approaches without tumor biopsy. Recent advances include microarray analysis of miRNAs, circulating miRNAs, karyotype analysis, and proteomic profiling. However, due to genomic instability and limited accessibility to tumor tissue, none of these biomarkers is widely used as a confirmed diagnostic method. Therefore, further research should identify specific tumor-derived molecular biomarkers to improve diagnostic and therapeutic strategies.

کلیدواژه ها:

Retinoblastoma ، molecular diagnosis ، cancer ، miRNA