Retinoblastoma

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Definition

Retinoblastoma is a cancer of the retina. Development of this tumor is initiated by mutations that inactivate both copies of the RB1 gene, which codes for the retinoblastoma protein.1,2

Epidemiology

Rb occurs mostly in children younger than 5 years and accounts for about 3% of the cancers occurring in children younger than 15 years. Adult cases have also been clinically recorded. 3 The estimated annual incidence is approximately 4 per million children.4 It begins with white blotches in one or both eyes (leukocoria) which can be seen in photographs (this is distinct from the red-eye effect which is normal); or when light reflects off the eye, as when watching television.

The tumor may begin in one or both eyes. Retinoblastoma is usually confined to the eye but can spread to the brain via the optic nerve.

As the retina is the light-sensitive part of the eye necessary for vision, loss of vision occurs.

Treatment

Until recently the only treatment was to surgically remove the affected eye before the cancer spread. Enucleation is still the treatment of choice for most unilateral cases. Affected children in developing countries present with advanced features and usually die of metastatic spread. In its initial stages, retinoblastoma is very similar to Coats' Disease, a non-cancerous retina disease. Coats' Disease should be ruled out before enucleation is done. A mis-diagnosis of Retinoblastoma accounts for the greatest number of Coats' disease eyes being enucleated.

Many children with bilateral retinoblastoma can be treated with a preservation attempt. Tumor chemoreduction with carboplatin and other drugs may reduce the tumor volume making them amenable to local therapies.5

Local therapies

  • Laser therapy - Uses infrared laser light to precisely destroy the blood vessels surrounding a tumor.
  • Cryotherapy - Use of a cold gas which is injected into the affected part of the retina to shrink the tumor.
  • Thermotherapy - A relatively new technique used mainly in new testing. It uses the principle that if heat is applied to the affected area, a tumor will sustain more damage than healthy cells because healthy cells can cool themselves better using healthy surrounding blood vessels. If this technique is not immediately successful it may increase the efficacy of other treatments such as chemotherapy and focused radiation plaques.
  • Radiotherapy - Generally used as a last resort, radiotherapy was previously the treatment of choice before the above mentioned treatments were developed. Radiotherapy destroys cancerous growths using gamma radiation but it carries with it many drawbacks, including:
    • Possibility of secondary cancerous growths which present themselves months or years later.
    • Destruction of healthy cells in the area surrounding the treated tumor.
    • Bone deformation due to the destruction of the growth plates mainly in the area of the temple.
  • Brachytherapy with beta-emitting eye applicators have also been a successful major treatment.
  • BEBIG (GmbH-Berlin-Germany) produces various kinds of ruthenium ophthalmic applicators for treating retinoblastoma.


References

  1. Knudson A (1971). "Mutation and cancer: statistical study of retinoblastoma". Proc Natl Acad Sci U S A 68 (4): 820-3. PMID 5279523.
  2. Friend S, Bernards R, Rogelj S, Weinberg R, Rapaport J, Albert D, Dryja T. "A human DNA segment with properties of the gene that predisposes to retinoblastoma and osteosarcoma". Nature 323 (6089): 643-6. PMID 2877398.
  3. Takahashi T, Tamura S, Inoue M, Isayama Y, Sashikata T (1983). "Retinoblastoma in a 26-year-old adult". Ophthalmology 90 (2): 179-83. PMID 6856254.
  4. Retinoblastoma Statistics at Cancer.org
  5. Dunkel IJ, Lee TC, Shi W, Beaverson KL, Novetsky D, Lyden D, Finlay JL, McCormick B, Abramson DH.. "A phase II trial of carboplatin for intraocular retinoblastoma.". Pediatr Blood Cancer.. PMID 17301956.

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