PATTERNS OF METASTATIC SPREAD, ORGAN SPECIFICITY, TIMING OF RECURRENT DISEASE, AND COMPLICATIONS CONFRONTED WITH METASTASIS

Retinoblastoma is the most common type of primary intraocular pediatric tumor. The incidence of retinoblastoma is approximately 1 in 20,000 live births, and it is estimated that there are about 300 to 350 new cases each year in the United States.

There are two forms of retinoblastoma. The most common form of retinoblastoma, known as unilateral disease, presents with a single tumor focus at a median age of about twenty-four months. Patients may also present with multiple tumor foci, usually in both eyes (bilateral disease), at a median age of about twelve months. The recognition of the earlier presentation of bilateral disease led to the classic two-hit hypothesis of retinoblastoma etiology [1]; in 1986 the “hit” was discovered to be a mutation in the RB1 gene on chromosome 13q14 [2]. It is currently believed that all patients with bilateral disease have a germline mutation in RB1, whereas most patients (about 85%) with unilateral disease have a sporadic mutation in the tumor cells only [3]. DNA sequencing to identify the mutation can be performed at specialized laboratories and is clinically useful to identify survivors of unilateral disease who may be at risk for other cancers later in life (secondary malignancy) and/or transmission of the disease to their offspring, to determine which relatives or offspring of survivors inherit the mutation and need to be carefully clinically screened, and to allow survivors with a germline mutation the option of considering preimplantation genetic diagnosis and in vitro fertilization to avoid the risk of transmitting the mutated RB1 to their offspring [4].