Using RB1 mutations to assess minimal residual disease in metastatic retinoblastoma

Liquid biopsy in Retinoblastoma: A review

PURPOSE

Retinoblastoma (RB) is the most common intraocular malignancy in children. The diagnosis of RB is mainly based on clinical features and imaging characteristics. Prognosis is based on stage of disease and response to treatment. In salvaged globes, direct tumor biopsy for genetic analysis and prognostication is an absolute contraindication at this point of time for the fear of extraocular tumor spread. Currently, there is a search for surrogate markers to allow accurate diagnosis and for prognostication, to predict the chances of globe salvage in RB. Therefore, biofluids such as plasma or aqueous humor have been studied to detect circulating tumor DNA (ctDNA) or cell-free DNA (cfDNA), respectively, to allow for treatment decision making, monitoring treatment response, and prognostic counselling.

METHODS

A search of electronic databases (PubMed, Google Scholar and MEDLINE) of all articles on liquid biopsy in retinoblastoma published in English was performed. The keywords used for the search included "retinoblastoma", "liquid biopsy", "aqueous humor" "circulating tumor cells", "cell-free DNA", "cfDNA", "circulating tumor DNA", "ctDNA", "tumor fraction", "RB1 mutation" and "SNCA". Additionally, historic articles on the advent of liquid biopsy in medicine were also reviewed. Pertinent cross-references from the studies were reviewed. Retrospective interventional and observational case series, observational case series, prospective cohort studies, reviews, case reports, surgical techniques, invited commentary and letters were included.

RESULTS

A total of 40 relevant articles were selected. Biomarkers in aqueous humor, serum and cerebrospinal fluid and their clinical applications are discussed.

CONCLUSION

Harvesting aqueous humor from eyes with retinoblastoma has been found safe and superior to blood for the detection of chromosomal changes. cfDNA from aqueous can be a surrogate marker to detect somatic copy number alterations and other genetic alterations in RB. ctDNA in plasma also has potential to help in diagnosis and prognosis of RB. Liquid biopsy in RB is an emerging topic, which could pave way for a better understanding of mechanisms for treatment response, resistance and recurrence in RB as well as possibly provide specific therapeutic targets to improve globe salvage.

Adjuvant therapy of histopathological risk factors of retinoblastoma in Europe: A survey by the European Retinoblastoma Group (EURbG)

INTRODUCTION

Advanced intraocular retinoblastoma can be cured by enucleation, but spread of retinoblastoma cells beyond the natural limits of the eye is related to a high mortality. Adjuvant therapy after enucleation has been shown to prevent metastasis in children with risk factors for extraocular retinoblastoma. However, histological criteria and adjuvant treatment regimens vary and there is no unifying consensus on the optimal choice of treatment.

METHOD

Data on guidelines for adjuvant treatment in European retinoblastoma referral centres were collected in an online survey among all members of the European Retinoblastoma Group (EURbG) network. Extended information was gathered via personal email communication.

RESULTS

Data were collected from 26 centres in 17 countries. Guidelines for adjuvant treatment were in place at 92.3% of retinoblastoma centres. There was a consensus on indication for and intensity of adjuvant treatment among more than 80% of all centres. The majority of centres use no adjuvant treatment for isolated focal choroidal invasion or prelaminar optic nerve invasion. Patients with massive choroidal invasion or postlaminar optic nerve invasion receive adjuvant chemotherapy, while microscopic invasion of the resection margin of the optic nerve or extension through the sclera are treated with combined chemo- and radiotherapy.

CONCLUSION

Indications and adjuvant treatment regimens in European retinoblastoma referral centres are similar but not uniform. Further biomarkers in addition to histopathological risk factors could improve treatment stratification. The high consensus in European centres is an excellent foundation for a common European study with prospective validation of new biomarkers.

Simultaneous identification of clinically relevant RB1 mutations and copy number alterations in aqueous humor of retinoblastoma eyes

BACKGROUND

Detection of germline RB1 mutations is critical for risk assessment of retinoblastoma (RB) patients. Assessment of somatic copy number alterations (SCNAs) is also critically important because of their prognostic significance. Herein we present a refined approach for the simultaneous identification of RB1 variants and SCNAs in the aqueous humor (AH) of RB eyes.

MATERIALS AND METHODS

Subjects included 7 eyes of 6 RB patients that underwent AH extraction, and 4 matched tumor samples. Cell-free DNA (cfDNA) was isolated and sequenced to assess genome-wide SCNAs. The same sequencing libraries then underwent targeted resequencing and mutation detection using a custom hybridization panel that targets RB1 and MYCN. Illumina paired-end 2x150bp sequencing was used to characterize single-nucleotide variants (SNVs) and loss of heterozygosity (LOH). Results were compared to peripheral blood RB1 testing. Tumor fraction (TFx) was calculated using ichorCNA.

RESULTS

Four of 7 AH samples contained clinically significant SCNAs. Of the 3 other samples, 1 showed focal MYCN amplification and 1 showed focal RB1 deletion. All 4 enucleated tumors contained SCNAs. Mutational analysis of tumor DNA identified all first hits (2 germline RB1 SNVs, 2 germline CNAs) and second hits (4 RB1 SNVs). RB1 variants in AH were concordant with those obtained from corresponding tumor tissue and blood. In AH samples without paired tumor, both RB1 hits were identified with high variant allele frequency, even in the absence of SCNAs.

CONCLUSIONS

AH liquid biopsy is a minimally invasive, in vivo alternative to tissue analysis for the simultaneous identification of RB1 variants and SCNAs in RB eyes.

Full-width postlaminar optic nerve tumor invasion of retinoblastoma as risk-factor for leptomeningeal spread of retinoblastoma. A case report and review of the literature

We present a 6-year-old boy with unilateral retinoblastoma of the left eye. MRI showed an intraocular tumor that extended into the optic nerve beyond the lamina cribrosa. The affected eye was enucleated and the optic nerve resection margin proved to be free. Following protocol, this patient received six courses of adjuvant systemic chemotherapy. Unfortunately, after 5 months this patient returned with the leptomeningeal spread of the tumor and died quickly thereafter.Histopathologic analysis of the enucleated eye and distal optic nerve revealed that the postlaminar tumor cells occupied the entire width of the optic nerve, extending all the way up to the pia mater, whereas, more often the tumor invasion is restricted to the center of the optic nerve. This was also visible on the MR images where contrast enhancement occupied the entire nerve width. A resection margin with tumor cells is recognized as a risk factor for metastasis, but perhaps the proximity of tumor cells to the leptomeninges should also be judged with caution as a potential increased risk for metastatic spread.

Retinoblastoma, the visible CNS tumor: A review

The pediatric ocular cancer retinoblastoma is the only central nervous system (CNS) tumor readily observed without specialized equipment: it can be seen by, and in, the naked eye. This accessibility enables unique imaging modalities. Here, we review this cancer for a neuroscience audience, highlighting these clinical and research imaging options, including fundus imaging, optical coherence tomography, ultrasound, and magnetic resonance imaging. We also discuss the subtype of retinoblastoma driven by the MYCN oncogene more commonly associated with neuroblastoma, and consider trilateral retinoblastoma, in which an intracranial tumor arises along with ocular tumors in patients with germline RB1 gene mutations. Retinoblastoma research and clinical care can offer insights applicable to CNS malignancies, and also benefit from approaches developed elsewhere in the CNS.

Retinoblastoma genetics in India: From research to implementation

Retinoblastoma is the prototypic genetic cancer. India carries the biggest burden of retinoblastoma globally, with an estimated 1500 new cases annually. Recent advances in retinoblastoma genetics are reviewed, focusing specifically on information with clinical significance to patients. The Indian literature on retinoblastoma clinical genetics is also highlighted, with a comment on challenges and future directions. The review concludes with recommendations to help clinicians implement and translate retinoblastoma genetics to their practice.

Molecular analysis distinguishes metastatic disease from second cancers in patients with retinoblastoma

The pediatric ocular tumor retinoblastoma readily metastasizes, but these lesions can masquerade as histologically similar pediatric small round blue cell tumors. Since 98% of retinoblastomas have RB1 mutations and a characteristic genomic copy number "signature", genetic analysis is an appealing adjunct to histopathology to distinguish retinoblastoma metastasis from second primary cancer in retinoblastoma patients. Here, we describe such an approach in two retinoblastoma cases. In patient one, allele-specific (AS)-PCR for a somatic nonsense mutation confirmed that a temple mass was metastatic retinoblastoma. In a second patient, a rib mass shared somatic copy number gains and losses with the primary tumor. For definitive diagnosis, however, an RB1 mutation was needed, but heterozygous promoter→exon 11 deletion was the only RB1 mutation detected in the primary tumor. We used a novel application of inverse PCR to identify the deletion breakpoint. Subsequently, AS-PCR designed for the breakpoint confirmed that the rib mass was metastatic retinoblastoma. These cases demonstrate that personalized molecular testing can confirm retinoblastoma metastases and rule out a second primary cancer, thereby helping to direct the clinical management.

Retinoblastoma

Retinoblastoma is the most common primary intraocular malignancy of childhood. It typically presents with leukocoria or strabismus. In later stages of the disease, the child may exhibit proptosis, buphthalmos, or hypopyon. The pathognomonic molecular aberration is a loss of function mutation in the RB1 gene on chromosome 13q. The degree of tumor involvement within the eye is defined by its group. Grouping was historically done with Reese-Ellsworth System. Recent therapeutic advances have led to the development of a new grouping system, the International Classification of Retinoblastoma (ICRB). In cases of extraocular extension and metastatic disease, the degree of tumor involvement outside of the eye is defined by its stage. Retinoblastoma is staged using the International Retinoblastoma Staging System (IRSS). Children with intraocular retinoblastoma have an excellent overall and ocular survival. In order to avoid the morbidity of enucleation and external beam radiation, treatments for isolated intraocular retinoblastoma have progressively moved toward targeted local modalities. Patients with extraocular involvement, such as those with trilateral retinoblastoma, have a poorer prognosis. The majority of these higher stage patients are now able to be cured with combination chemotherapy.

Management of retinoblastoma in children: current status

In recent years, there have been dramatic changes in the management of intraocular retinoblastoma. Intraocular retinoblastoma is a highly curable malignancy and current treatments are aimed to preserve vision while reducing the late effects such as treatment-induced secondary malignancies. The advent of intra-arterial chemotherapy changed the treatment paradigm from systemic treatment with chemotherapy to local treatment, and new questions emerged. While intra-arterial chemotherapy achieved encouraging results, only experience from major referral centers is reported, so its indications, advantages and risks are still to be elucidated. Many factors should be considered when choosing the appropriate conservative therapy. When the disease has extended outside the eye, the chances of cure are significantly lower and treatment should be tailored by the presence of pathology risk factors such as invasion of the choroid, the optic nerve, and the sclera. Adjuvant therapy is decided upon this information. Children with overt extraocular disease are treated with higher dose neoadjuvant therapy followed by delayed enucleation and adjuvant therapy.

The genomic landscape of retinoblastoma: a review

Retinoblastoma is a paediatric ocular tumour that continues to reveal much about the genetic basis of cancer development. Study of genomic aberrations in retinoblastoma tumours has exposed important mechanisms of cancer development and identified oncogenes and tumour suppressors that offer potential points of therapeutic intervention. The recent development of next-generation genomic technologies has allowed further refinement of the genomic landscape of retinoblastoma at high resolution. In a relatively short period of time, a wealth of genetic and epigenetic data has emerged on a small number of tumour samples. These data highlight the inherent molecular complexity of this cancer despite the fact that most retinoblastomas are initiated by the inactivation of a single tumour suppressor gene. This review outlines the current understanding of the genomic, genetic and epigenetic changes in retinoblastoma, highlighting recent genome-wide analyses that have identified exciting candidate genes worthy of further validation as potential prognostic and therapeutic targets.

Retinoblastoma

Retinoblastoma is an aggressive eye cancer of infancy and childhood. Survival and the chance of saving vision depend on severity of disease at presentation. Retinoblastoma was the first tumour to draw attention to the genetic aetiology of cancer. Despite good understanding of its aetiology, mortality from retinoblastoma is about 70% in countries of low and middle income, where most affected children live. Poor public and medical awareness, and an absence of rigorous clinical trials to assess innovative treatments impede progress. Worldwide, most of the estimated 9000 newly diagnosed patients every year will die. However, global digital communications present opportunities to optimise standards of care for children and families affected by this rare and often devastating cancer. Parents are now leading the effort for widespread awareness of the danger of leucocoria. Genome-level technologies could make genetic testing a reality for every family affected by retinoblastoma. Best-practice guidelines, online sharing of pathological images, point-of-care data entry, multidisciplinary research, and clinical trials can reduce mortality. Most importantly, active participation of survivors and families will ensure that the whole wellbeing of the child is prioritised in any treatment plan.

Epidemiology and Rb1 gene of retinoblastoma

Retinoblastoma (Rb) is the most common eye cancer in children and it can be inherited. Rb is quite rare and originators from the neural retina with a significant genetic component in etiology, which occurs in approximately 1 in every 20 0000 births. In children with the heritable genetic form of Rb, there is a mutation on chromosome 13, called the retinoblastoma 1 (Rb1) gene. Early diagnosis and intervention is critical to the successful treatment of the Rb. The Rb1 gene is the first cloned tumor suppressor gene. As a negative regulator of the cell cycle, Rb1 gene could maintain a balance between cell growth and development through binding to transcription factors and regulating the expression of genes involved in cell proliferation and differentiation. Thus, it is involved in cell cycle, cell senescence, growth arrest, apoptosis and differentiation. We summarized the recent advances on the epidemiology and Rb1 gene of Rb in this review.