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Genetic testing and counselling

TL;DR — Testing should establish whether an RB1 predisposition is constitutional, mosaic or confined to tumour tissue. Blood-only negative testing is least informative in unilateral disease when tumour is unavailable; paired tumour–blood analysis can identify both somatic hits and materially reduce residual heritable risk. Assay design matters because low-level mosaic variants and copy-number changes can evade limited methods. Results direct surveillance for the child, cascade testing, reproductive counselling and lifelong survivorship planning.

Decision-relevant evidence

  • AACR predisposition recommendations estimate heritable disease in about 45% of affected children and link germline variants to bilateral, trilateral and later-neoplasm risks; the same lineage in 2017 gave about 40% and an approximately 20% second-cancer risk, so the year of the recommendation must be cited with the number (Kamihara 2025, PMID 39998650; Kamihara 2017, PMID 28674118).

  • Testing order matters more than testing technology. The preferred workflow for a proband is to sequence tumour tissue first when it is available, then interrogate peripheral-blood leukocyte DNA for the specific variants found in the tumour to establish germline status; blood alone is tested only when no tumour tissue exists, and at-risk relatives are then tested by targeted sequencing for that specific variant (Lindquist 2025, PMID 40993897).

  • Yield tracks laterality, so a negative blood test means different things in different children: germline detection reached 86.2% in bilateral versus 19% in unilateral disease in a 50-child Indian series using next-generation sequencing plus MLPA, and the mutation-positive group had significantly more recurrence (P = 0.021) and progression (P < 0.001) (Gupta 2021, PMID 34294096).

  • Constitutional variants are present in a minority of isolated unilateral cases and some are mosaic: 6 of 36 mutation-informative unilateral patients (17%) carried a constitutional mutation, with mosaicism demonstrated in one and suspected in two more (Lohmann 1997, PMID 9311732).

  • Mosaicism is the main reason a standard germline assay under-calls heritable disease. Paired plasma cell-free DNA and buffy-coat sequencing in 136 consecutive patients found RB1 mosaicism in 20 (14.7%), including four who had tested germline-negative elsewhere; mosaic patients were bilateral in 55.0% versus 91.7% of heterozygous patients (difference 36.7%, 95% CI 13.8–59.6; P = .002) (Gao 2025, PMID 40338593; commentary Chévez-Barrios 2025, PMID 40338597).

  • Mosaicism also creates a specific interpretive trap in disease monitoring: the mosaic variant remained detectable in cell-free DNA after treatment, with allele fraction falling and then plateauing at mosaic levels in the absence of clinical disease. Reading that plateau as residual tumour risks overtreatment (PMID 40338593).

  • Counselling numbers for unaffected parents can be stated concretely. Deep sequencing of both parents of 124 consecutive bilateral probands identified one mosaic parent, bounding recurrence risk from parental mosaicism at 0.4%, with an observed-recurrence estimate of 0.8% — 266- to 533-fold above population risk, and small enough that most such couples are counselled toward surveillance rather than intervention (Dehainault 2017, PMID 28000698).

  • A germline result partitions surveillance rather than merely labelling a family: carriers require intensive intraocular examination and brain imaging in infancy, non-carriers require none, and the AJCC "H" category exists precisely to carry this into staging (Mallipatna 2016, PMID 27488068; Abu-Amero 2025, PMID 41009976).

  • Assay design has to cover more than point mutations. A single-platform next-generation sequencing method detects point mutations, small indels and large deletions or duplications across RB1 together with MYCN amplification within three days from DNA extraction to interpretation, and detects low-level mosaic variants that routine Sanger sequencing misses (Li 2016, PMID 27155049). Reported RB1 variation includes nonsense, small insertion/deletion and splice variants, copy-number alterations and promoter methylation, so a workflow limited to exonic sequencing will systematically under-ascertain (Nag 2025, PMID 40235228).

  • Aqueous-humour and plasma cell-free DNA give pre-therapeutic access to tumour genotype in a tumour that must not be biopsied, and are being evaluated for constitutional-status assessment, molecular risk stratification and treatment monitoring — currently as a research and specialist-laboratory pathway rather than an established standard (Bouchoucha 2023, PMID 36470558).

  • Testing is not the rate-limiting step everywhere. In low- and middle-income settings the binding constraints are late presentation, referral pathways and treatment abandonment; systematic population screening is judged infeasible outside families with a germline RB1 variant or a family history, and strengthening referral and abandonment-reduction is argued to be more effective than universal screening (Chantada 2025, PMID 40619694). Reproductive counselling therefore has to be deliverable where comprehensive testing is not.

Clinical and research frame

Domain Operational meaning Evidence boundary
Bilateral/multifocal child Blood comprehensive RB1 test Treat as heritable while unresolved
Unilateral child; tumour available Paired tumour and blood Best route to distinguish somatic-only from constitutional
Blood negative; tumour unavailable Residual-risk counselling Negative is not equivalent to two proven somatic hits
Known family variant Targeted cascade/prenatal testing Variant-specific and consent-led
Low-level signal Orthogonal confirmation Mosaic fraction affects interpretation

Interpretation rules

  • Keep the child-level endpoints of survival and metastasis separate from the eye-level endpoint of globe salvage.

  • Report initial stage, laterality, heritability, prior treatment and follow-up; otherwise comparisons are not transportable.

  • A retrospective eye series estimates performance in selected eyes; it does not establish superiority over another route.

  • Absence of metastasis in a small series is a safety observation, not proof that risk is zero.

  • Treatment-era effects matter because external-beam radiotherapy, systemic chemotherapy, IAC and intravitreal therapy create different late-risk profiles.

  • Income stratum and access are effect modifiers, not background descriptors (Global Retinoblastoma Study Group 2022, PMID 35839812).

Evidence register

The following records were each retrieved live from PubMed E-utilities on 2026-09-01 and re-fetched live during the independent audit on the same date. Every identifier below resolved, and its author, year, journal and title matched the citation as written. Inclusion records the evidence base for this page; a register entry asserts that the record exists and is on topic, not that it supports a specific effect estimate.

PMID Year Study or review Role in this page
27155049 2016 A Rapid and Sensitive Next-Generation Sequencing Method to Detect RB1 Mutations Improves Care for Retinoblastoma Patients and Their Families. Topic-resolved source (Li 2016, PMID 27155049)
9311732 1997 Constitutional RB1-gene mutations in patients with isolated unilateral retinoblastoma. Topic-resolved source (Lohmann 1997, PMID 9311732)
39998650 2025 Update on Retinoblastoma Predisposition and Surveillance Recommendations for Children. Topic-resolved source (Kamihara 2025, PMID 39998650)
32422154 2020 Recommendations for Long-Term Follow-up of Adults with Heritable Retinoblastoma. Topic-resolved source (Tonorezos 2020, PMID 32422154)
35839812 2022 The Global Retinoblastoma Outcome Study: a prospective, cluster-based analysis of 4064 patients from 149 countries. Topic-resolved source (Global 2022, PMID 35839812)
38804799 2024 Retinoblastoma - A comprehensive review, update and recent advances. Topic-resolved source (Nag 2024, PMID 38804799)
37667345 2023 Retinoblastoma: present scenario and future challenges. Topic-resolved source (Byroju 2023, PMID 37667345)
35969246 2022 [Imaging of retinoblastoma : Current state-of-the-art and future prospects]. Topic-resolved source (Schweiger 2022, PMID 35969246)
28695165 2017 Neonatal Retinoblastoma. Topic-resolved source (Kivelä 2017, PMID 28695165)
22414599 2012 Retinoblastoma. Topic-resolved source (Dimaras 2012, PMID 22414599)
16570739 2006 Retinoblastoma. Topic-resolved source (Melamud 2006, PMID 16570739)
27488068 2016 Genetics of Retinoblastoma. Topic-resolved source (Mallipatna 2016, PMID 27488068)
33583507 2021 Neonatal Retinoblastoma. Topic-resolved source (Lin 2021, PMID 33583507)
40731848 2025 Update on Retinoblastoma Therapies. Topic-resolved source (Martínez 2025, PMID 40731848)
34210807 2021 Update on the Treatment of Retinoblastoma. Topic-resolved source (Manrique 2021, PMID 34210807)
29321667 2018 The management of retinoblastoma. Topic-resolved source (Fabian 2018, PMID 29321667)
40993897 2025 Retinoblastoma: Advances in Genetic Testing. Topic-resolved source (Lindquist 2025, PMID 40993897)
26969537 2016 Retinoblastoma: An update. Topic-resolved source (Delhiwala 2016, PMID 26969537)
10761080 1998 Retinoblastoma. Topic-resolved source (Margo 1998, PMID 10761080)
38492167 2024 Epidemiology, Diagnosis and Genetics of Retinoblastoma: ICMR Consensus Guidelines. Topic-resolved source (Singh 2024, PMID 38492167)
40235228 2025 Genetics of Retinoblastoma - An Update. Topic-resolved source (Nag 2025, PMID 40235228)
36470558 2023 Retinoblastoma: From genes to patient care. Topic-resolved source (Bouchoucha 2023, PMID 36470558)
3323180 1987 Intraocular and extraocular retinoblastoma. Topic-resolved source (Grabowski 1987, PMID 3323180)
37658463 2023 Genetics in ophthalmology: molecular blueprints of retinoblastoma. Topic-resolved source (Marković 2023, PMID 37658463)
27189421 2015 Retinoblastoma. Topic-resolved source (Dimaras 2015, PMID 27189421)
38615905 2024 Recent progress in retinoblastoma: Pathogenesis, presentation, diagnosis and management. Topic-resolved source (Zhou 2024, PMID 38615905)
25435120 2015 Retinoblastoma. Topic-resolved source (Rodriguez-Galindo 2015, PMID 25435120)
16934146 2006 Retinoblastoma. Topic-resolved source (Aerts 2006, PMID 16934146)
20687510 2010 Retinoblastoma. Topic-resolved source (Lohmann 2010, PMID 20687510)
35412907 2022 Hereditary retinoblastoma iPSC model reveals aberrant spliceosome function driving bone malignancies. Topic-resolved source (Tu 2022, PMID 35412907)
36408154 2022 Retinoblastoma: Review and new insights. Topic-resolved source (Cruz-Gálvez 2022, PMID 36408154)
28674118 2017 Retinoblastoma and Neuroblastoma Predisposition and Surveillance. Topic-resolved source (Kamihara 2017, PMID 28674118)
26679524 2016 [Retinoblastoma update]. Topic-resolved source (Aerts 2016, PMID 26679524)
24793631 2014 [Retinoblastoma: recent advances]. Topic-resolved source (Jehanne 2014, PMID 24793631)
40338597 2025 DNA Assays to Detect and Characterize RB1 Mosaicism in Retinoblastoma. Topic-resolved source (Chévez-Barrios 2025, PMID 40338597)
40338593 2025 Detection and Characterization of RB1 Mosaicism in Patients With Retinoblastoma Receiving cfDNA Test. Topic-resolved source (Gao 2025, PMID 40338593)
40619694 2025 Challenges for Early Diagnosis in Retinoblastoma in Low- and Middle-Income Countries. Topic-resolved source (Chantada 2025, PMID 40619694)
28000698 2017 Mosaicism and prenatal diagnosis options: insights from retinoblastoma. Topic-resolved source (Dehainault 2017, PMID 28000698)
34294096 2021 Retinoblastoma genetics screening and clinical management. Topic-resolved source (Gupta 2021, PMID 34294096)
33120616 2020 Modern treatment of retinoblastoma: A 2020 review. Topic-resolved source (Ancona-Lezama 2020, PMID 33120616)
41009976 2025 Genetics of Retinoblastoma: An Overview and Significance of Genetic Testing in Clinical Practice. Added by audit 2026-09-01 (Abu-Amero 2025, PMID 41009976)

Source chronology

Era marker PMID What the record contributes
1987 3323180 Intraocular and extraocular retinoblastoma. (Grabowski 1987, PMID 3323180)
1997 9311732 Constitutional RB1-gene mutations in patients with isolated unilateral retinoblastoma. (Lohmann 1997, PMID 9311732)
1998 10761080 Retinoblastoma. (Margo 1998, PMID 10761080)
2006 16570739 Retinoblastoma. (Melamud 2006, PMID 16570739)
2006 16934146 Retinoblastoma. (Aerts 2006, PMID 16934146)
2010 20687510 Retinoblastoma. (Lohmann 2010, PMID 20687510)
2012 22414599 Retinoblastoma. (Dimaras 2012, PMID 22414599)
2014 24793631 [Retinoblastoma: recent advances]. (Jehanne 2014, PMID 24793631)
2015 25435120 Retinoblastoma. (Rodriguez-Galindo 2015, PMID 25435120)
2015 27189421 Retinoblastoma. (Dimaras 2015, PMID 27189421)
2016 26679524 [Retinoblastoma update]. (Aerts 2016, PMID 26679524)
2016 26969537 Retinoblastoma: An update. (Delhiwala 2016, PMID 26969537)
2016 27155049 A Rapid and Sensitive Next-Generation Sequencing Method to Detect RB1 Mutations Improves Care for Retinoblastoma Patients and Their Families. (Li 2016, PMID 27155049)
2016 27488068 Genetics of Retinoblastoma. (Mallipatna 2016, PMID 27488068)
2017 28000698 Mosaicism and prenatal diagnosis options: insights from retinoblastoma. (Dehainault 2017, PMID 28000698)

Evidence limitations

  • Most intraocular treatment evidence is observational, single-centre and reported per eye; bilateral eyes within one child are statistically correlated.

  • Classification and treatment changed over time, producing stage migration and confounding by indication.

  • Rare metastatic and late-effect outcomes require multinational cohorts and decades of follow-up.

  • Verification is abstract-level. Every claim on this page was checked against the abstract of the record it cites during the independent audit on 2026-09-01; where an abstract could not support a claim, the claim was removed or restated as an explicit limit. Claims requiring full text beyond the abstract are not made here.

Open questions

  • How does real-world assay sensitivity vary outside reference laboratories? The current evidence register defines the design space but does not close the question.

  • What residual-risk threshold should alter examinations under anaesthesia? The current evidence register defines the design space but does not close the question.

  • How are reproductive options accessed across income settings? The current evidence register defines the design space but does not close the question.

References

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  2. Lohmann DR, et al. Constitutional RB1-gene mutations in patients with isolated unilateral retinoblastoma. American journal of human genetics. 1997;61:282-94. PMID 9311732
  3. Kamihara J, et al. Update on Retinoblastoma Predisposition and Surveillance Recommendations for Children. Clinical cancer research : an official journal of the American Association for Cancer Research. 2025;31:1573-1579. PMID 39998650
  4. Tonorezos ES, et al. Recommendations for Long-Term Follow-up of Adults with Heritable Retinoblastoma. Ophthalmology. 2020;127:1549-1557. PMID 32422154
  5. Global Retinoblastoma Study Group. The Global Retinoblastoma Outcome Study: a prospective, cluster-based analysis of 4064 patients from 149 countries. The Lancet. Global health. 2022;10:e1128-e1140. PMID 35839812
  6. Nag A, et al. Retinoblastoma - A comprehensive review, update and recent advances. Indian journal of ophthalmology. 2024;72:778-788. PMID 38804799
  7. Byroju VV, et al. Retinoblastoma: present scenario and future challenges. Cell communication and signaling : CCS. 2023;21:226. PMID 37667345
  8. Schweiger B, et al. [Imaging of retinoblastoma : Current state-of-the-art and future prospects]. Radiologie (Heidelberg, Germany). 2022;62:1067-1074. PMID 35969246
  9. Kivelä TT, et al. Neonatal Retinoblastoma. Asia-Pacific journal of oncology nursing. 2017;4:197-204. PMID 28695165
  10. Dimaras H, et al. Retinoblastoma. Lancet (London, England). 2012;379:1436-46. PMID 22414599
  11. Melamud A, et al. Retinoblastoma. American family physician. 2006;73:1039-44. PMID 16570739
  12. Mallipatna A, et al. Genetics of Retinoblastoma. Asia-Pacific journal of ophthalmology (Philadelphia, Pa.). 2016;5:260-4. PMID 27488068
  13. Lin FY, et al. Neonatal Retinoblastoma. Clinics in perinatology. 2021;48:53-70. PMID 33583507
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  15. Manrique M, et al. Update on the Treatment of Retinoblastoma. NeoReviews. 2021;22:e423-e437. PMID 34210807
  16. Fabian ID, et al. The management of retinoblastoma. Oncogene. 2018;37:1551-1560. PMID 29321667
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