Classification
There are two forms of the disease; a heritable form and non-heritable form (all cancers are considered genetic in that mutations of the genome are required for their development, but this does not imply that they are heritable, or transmitted to offspring). Approximately 55% of children with Rb have the non-heritable form. If there is no history of the disease within the family, the disease is labeled "sporadic", but this does not necessarily indicate that it is the non-heritable form.
In about two thirds of cases, only one eye is affected (unilateral retinoblastoma); in the other third, tumours develop in both eyes (bilateral retinoblastoma). The number and size of tumours on each eye may vary. In certain cases, the pineal gland is also affected (trilateral retinoblastoma). The position, size and quantity of tumours are considered when choosing the type of treatment for the disease.
Read more about this topic: Retinoblastoma