Description

Retinoblastoma is a malignant tumor of the retina and is the most common intraocular tumor in children. It is caused by an RB1 gene mutation at 13q14, which can be germline or somatic.

Epidemiology

• In the United States, retinoblastoma occurs approximately once in every 18,000 live births.
• Approximately 300 new pediatric cases of retinoblastoma are diagnosed each year in the United States, which represents 3% of all childhood cancers.
• 25% of patients will present with bilateral disease at diagnosis, which signifies germline retinoblastoma. 40% of all retinoblastoma cases are germline, which most often presents with not only bilateral disease but also unilateral disease in 15%.
• Median age at diagnosis is 24 months in patients with unilateral disease and 12 months in patients with bilateral tumors.
• There is no association with race, gender, or laterality of eye involvement.
• The greatest disease burden is found in countries with the largest populations and high birth rates, such as Asia and Africa.

Risk Factors

• RB1 gene mutations are inherited in an autosomal dominant pattern.
• Family history of retinoblastoma in parents or siblings warrants early screening and genetic studies to determine the risk of disease.

General Prevention

Although there is no definite way to prevent retinoblastoma, careful eye exams during well-child examinations will allow earlier detection of the disease.

Pathophysiology

• Tumor development requires loss of function of the RB1 gene, which is a cell cycle regulator and resides in chromosome 13.
• Constitutional loss of one RB1 allele predisposes a patient to cancer. Loss of the second allele with other genetic or epigenetic changes in the retinal lesion will initiate formation of retinoblastoma.
• Somatic retinoblastoma has no germline RB1 mutation and thus requires biallelic inactivation of the RB1 gene in a single retinal cell.
• Other genetic changes have been described in tumor cells such as MYCN oncogene amplification.
• There are three common growth patterns:
  • Intraretinal (growth only in the retina)
  • Endophytic (inner surface of retina to vitreous)
  • Exophytic (outer surface of retina to subretinal space)
  • Tumor cells seeding from the primary mass to grow independently in the vitreous or subretinal space.
• Children with loss of RB1 with large chromosomal deletions of surrounding genes are at risk for developmental anomalies such as facial dysmorphism and mental and/or motor impairment (13q deletion syndrome).
• Patients with bilateral retinoblastoma are at risk for involvement of the pineal gland, termed “trilateral” retinoblastoma.

Etiology

Mutations in the RB1 gene predispose to retinoblastoma, pinealoblastoma, osteosarcoma, and other cancers.