Mussa Adil Butt MBBS BSc (Hons)1
1The Princess Alexandra Hospital, Harlow, United Kingdom
Introduction
Retinoblastoma is the most common childhood intraocular cancer. It originates from a mutation of the retinoblastoma (RB1) gene, a tumour-suppressor gene. Infants are usually diagnosed through an incidental finding of leukocoria. The disease is classified by size, location and number of tumours and it is used to determine treatment. Management includes surgery, radiotherapy, photocoagulation and chemotherapy. Early diagnosis and treatment is key to preserving vision and therefore a thorough understanding of the condition is important (1).
Aetiology
Retinoblastoma was first described by Knudson in 1971. He proposed a theory that retinoblastoma is caused by two mutational events. Loss or mutations of both RB1 alleles are required for the disease to develop. In hereditary cases, which account for 55% of cases, all cells carry a germline inactivated RB1 allele and the second allele is lost somatically in retinal cells. Germline RB1 mutations have a high penetrance rate and result in bilateral retinoblastoma. In non-hereditary cases, which account for 45% of cases, inactivation of both RB1 alleles occurs somatically in a single retinal progenitor cell, resulting in unilateral disease (2).
Symptoms and Diagnosis
Leukocoria is the most common presenting sign of retinoblastoma. This is usually detected by families on flash photography. Strabismus is the second most common presenting sign which is usually associated with visual impairment. The presentation of retinoblastoma is dependent on the stage of the disease and can be unilateral or bilateral. Fundus examination is essential for diagnosis and staging, this routinely is done under anaesthesia due to the young age of most patients. Screening is reserved for cases of familial history and known germline mutations (3).
Management
The aim of management in retinoblastoma is to preserve life, the eye and vision. Optimal management requires appropriate staging followed by close monitoring to measure progress and detect recurrence. There are several methods to manage retinoblastoma which can be organised as focal, local and systemic. Focal therapy is used for small tumours and local or systemic therapies are reserved for advanced retinoblastoma (4).
Focal therapy includes cryotherapy, laser photocoagulation and plaque brachytherapy. Cryotherapy, the use of extreme cold to freeze tissue, is used for small peripheral retinal tumours. Complications include retinal detachment and retinal tear. Cryotherapy is used before chemotherapy to increase delivery across the blood-retinal barrier. Laser photocoagulation uses lasers to burn and coagulate the blood supply to the tumour. Complications for photocoagulation also include retinal detachment, retinal hole and retinal traction. Photocoagulation is contraindicated while the patient is on active chemotherapy. Plaque brachytherapy involves the placement of a radioactive implant onto the sclera. This method allows focal radiation whilst minimising damage to surrounding structures (4).
Local therapy consists of external beam radiotherapy and enucleation. External beam radiotherapy was the preferred form of management in the late 1900s. It was later abandoned due to associated complications with secondary cancers as a direct result of the radiation. It is currently used for eyes where chemotherapy has failed or is contraindicated. Enucleation remains the treatment of choice for advanced intraocular retinoblastoma with neovascularization of iris, glaucoma, anterior chamber tumour invasion or vitreous haemorrhage. Chemotherapy, both intravitreal and intraarterial, is an integral part of retinoblastoma therapy to reduce tumour size (4).
Conclusion
Although rare, retinoblastoma is the most common childhood intraocular cancer. It has a strong genetic component and routinely presents as leukocoria. Diagnosis and subsequent classification are reliant on examination under anaesthesia. Management modalities are dependent on size, location and number of tumours as well other patient factors. Having a sound knowledge of the condition is key to early diagnosis and treatment and therefore preserving vision for patients.
References
1. Dimaras H, Kimani K, Dimba EAO, Gronsdahl P, White A, Chan HSL, et al. Retinoblastoma. Lancet. 2012 Apr 14;379(9824):1436–46.
2. Aerts I, Lumbroso-Le Rouic L, Gauthier-Villars M, Brisse H, Doz F, Desjardins L. Retinoblastoma. Orphanet J Rare Dis [Internet]. 2006 Aug 25 [cited 2021 Dec 3];1(1):1–11. Available from: https://link.springer.com/articles/10.1186/1750-1172-1-31
3. Rao R, Honavar SG. Retinoblastoma. Indian J Pediatr [Internet]. 2017 Dec 1 [cited 2021 Dec 3];84(12):937–44. Available from: https://link.springer.com/article/10.1007/s12098-017-2395-0
4. Pandey AN. Retinoblastoma: An overview. Saudi J Ophthalmol. 2014 Oct 1;28(4):310–5.