Retinoblastoma
Retinoblastoma (Rb) is a rare form of cancer that rapidly develops from the immature cells of a retina, the light-detecting tissue of the eye. It is the most common primary malignant intraocular cancer in children, and it is almost exclusively found in young children. Though most children survive this cancer, they may lose their vision in the affected eye(s) or need to have the eye removed. Almost half of children with retinoblastoma have a hereditary genetic defect associated with retinoblastoma. In other cases, it is caused by a congenital mutation in the chromosome 13 gene 13q14 (retinoblastoma protein ). Signs and symptoms. Retinoblastoma is universally known as the most intrusive intraocular cancer among children. The chance of survival and preservation of the eye depends fully on the severity. Retinoblastoma is extremely rare as there are only about 200 to 300 cases every year in the United States. Looking at retinoblastoma globally, only 1 in about 15,000 children have this malignancy but these numbers continuously increase. Intraocular malignancies are more curable rather than extraocular malignancies due to early diagnosis and an early treatment prognosis. During infant screenings, if they incorporate an eye screening like they do a hearing screening, it  can be detected at an earlier age, therefore, preventing its spread. Leucocoria is the primary indication of retinoblastoma and is when the cancer is still intraocular, meaning inside the eye. When light is reflected by the white tumor, the view of the red retina is blocked. Retinoblastoma can be curable after the initial sign and up to six months, if the tumor is intraocular. If you do not visit an ophthalmologist with signs of leucocoria within a reasonable amount of time, the delay in the diagnosis could lead to a more severe prognosis. Due to a delay in the diagnosis , it could result in proptosis which is then considered extraocular, the most severe. The most common and obvious sign of retinoblastoma is an abnormal appearance of the retina as viewed through the pupil, the medical term for which is leukocoria, also known as amaurotic cat's eye reflex. Other signs and symptoms include deterioration of vision, a red and irritated eye with glaucoma, and faltering growth or delayed development. Some children with retinoblastoma can develop a squint, commonly referred to as "cross-eyed" or "wall-eyed" (strabismus). Retinoblastoma presents with advanced disease in developing countries and eye enlargement is a  common finding. Depending on the position of the tumors, they may be visible during a simple eye exam using an ophthalmoscope to look through the pupil. A positive diagnosis is usually made only with an examination under anesthetic (). A white eye reflection is not always a positive indication of retinoblastoma and can be caused by light being reflected badly or by other conditions such as Coats' disease. The presence of the photographic fault red eye in only one eye and not in the other may be a sign of retinoblastoma. A clearer sign is "white eye" or "cat's eye  (leukocoria). Cause. Mutation of genes, found in chromosomes, can affect the way in which cells grow and develop within the body. Alterations in RB1 or MYCN can give rise to retinoblastoma. RB1. In children with the heritable genetic form of retinoblastoma, a mutation occurs in the RB1" gene on chromosome 13." RB1" was the first tumor suppressor gene cloned. Although" RB1" interacts with over 100 cell proteins, its negative regulator effect on the cell cycle principally arises from binding and inactivation of the transcription factor "E2F", thus repressing the transcription of genes which are required for the S phase. The  defective "RB1 "gene can be inherited from either parent; in some children, however, the mutation occurs in the early stages of fetal development. The expression of the" RB1 "allele is autosomal dominant with 90% penetrance. Inherited forms of retinoblastomas are more likely to be bilateral. In addition, inherited uni- or bilateral retinoblastomas may be associated with pineoblastoma and other malignant midline supratentorial primitive neuroectodermal tumors (PNETs) with a dismal outcome; retinoblastoma concurrent with a PNET is known as trilateral retinoblastoma. A recent meta-analysis has shown that survival of trilateral retinoblastoma has increased substantially over the last decades. The development  of retinoblastoma can be explained by the two-hit model. According to the two-hit model, both alleles need to be affected, so two events are necessary for the retinal cell or cells to develop into tumors. The first mutational event can be inherited (germline or constitutional), which will then be present in all cells in the body. The second “hit” results in the loss of the remaining normal allele (gene) and occurs within a particular retinal cell. In the sporadic, nonheritable form of retinoblastoma, both mutational events occur within a single retinal cell after fertilization (somatic events); sporadic retinoblastoma  tends to be unilateral. Several methods have been developed to detect the "RB1" gene mutations. Attempts to correlate gene mutations to the stage at presentation have not shown convincing evidence of a correlation. MYCN. Not all retinoblastoma cases are with RB1 inactivation. There are cases reported with only one RB1 mutation or even two functional RB1 alleles, which indicates other oncogenic lesions of retinoblastoma. Somatic amplification of the "MYCN" oncogene is responsible for some cases of nonhereditary, early-onset, aggressive, unilateral retinoblastoma. MYCN can act as a transcription factor and promotes proliferation by regulating the expression of cell cycle genes . Although "MYCN" amplification accounted for only 1.4% of retinoblastoma cases, researchers identified it in 18% of infants diagnosed at less than 6 months of age. Median age at diagnosis for "MYCN" retinoblastoma was 4.5 months, compared with 24 months for those who had nonfamilial unilateral disease with two "RB1 "gene mutations. Diagnosis. Screening for retinoblastoma should be part of a "well baby" screening for newborns during the first 3 months of life, to include: Classification. The two forms of the disease are a heritable form and nonheritable 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). Around 55% of children with retinoblastoma have the nonheritable form. If no history of the disease exists within the family, the disease is labeled "sporadic", but this does not necessarily indicate that it is the nonheritable form. Bilateral retinoblastomas are commonly heritable, while unilateral retinoblastomas are commonly nonheritable. In about two-thirds of cases, only one eye is affected (unilateral retinoblastoma); in the other third, tumors develop in both eyes (bilateral retinoblastoma). The number and size of tumors on each eye may vary . In certain cases, the pineal gland or the suprasellar or parasellar region (or in very rare cases other midline intracranial locations) is also affected (trilateral retinoblastoma). The position, size, and quantity of tumors are considered when choosing the type of treatment for the disease. Differential diagnosis. If the eye examination is abnormal, further testing may include imaging studies, such as computerized tomography (CT), magnetic resonance imaging (MRI), and ultrasound. CT and MRI can help define the structure abnormalities and reveal any calcium depositions. Ultrasound can help define the height and thickness of the tumor. Bone marrow examination or lumbar puncture  may also be done to determine any metastases to bones or the brain. Morphology. Gross and microscopic appearances of retinoblastoma are identical in both hereditary and sporadic types. Macroscopically, viable tumor cells are found near blood vessels, while zones of necrosis are found in relatively avascular areas. Microscopically, both undifferentiated and differentiated elements may be present. Undifferentiated elements appear as collections of small, round cells with hyperchromatic nuclei; differentiated elements include Flexner-Wintersteiner rosettes, Homer Wright rosettes, and fleurettes from photoreceptor differentiation. Genetic testing. Identifying the "RB1" gene mutation that led to a child's retinoblastoma can be important in  the clinical care of the affected individual and in the care of (future) siblings and offspring. It may run in the family. Imaging. Traditional ultrasound B scan can detect calcifications in the tumour while high-frequency ultrasound B scan is able to provide higher resolution than the traditional ultrasound and determine the proximity of the tumour with front portion of the eye. MRI scan can detect high-risk features such as optic nerve invasion; choroidal invasion, scleral invasion, and intracranial invasion. CT scan is generally avoided because radiation can stimulate the formation of more eye tumours in those with RB1  genetic mutation. Staging. In order to properly diagnose retinoblastoma, there must be guidelines to follow to properly classify the risk of the tumor. The "Reese Ellsworth Classification System," by Dr. Algernon Reese and Dr. Robert Ellsworth, is universally used to determine the size, location, and multi-focality of the tumor. The system was originally used to decide the best treatment result by using external beam radiotherapy, as well as, the likeliness of salvaging the globe of the eye. Due to chemotherapy not being part of the "Reese Ellsworth Classification System," there needed to be an updated classification system to foresee  the treatment outcomes of chemotherapy. The International Classification for Intraocular Retinoblastoma is now the current system being used, and it was created by Murphree and associates. According to Reese and Ellsworth, there were different groups that had various features in order to classify the globe salvage as very favorable to the category of very unfavorable. In order to salvage the affected eye, the disc diameter had to be around 4DD and behind the equator to have higher favorability. If the tumor was around ten in disc diameter and involved roughly 50% of the retina, it was considered unfavorable to salvage  the globe which could result in enucleation. According to Murphree, the different groups were classified from very low risk to very high risk which was determined by features of the given tumor. Very low risk means that the tumor has to be less than 3mm and there must be no seeding of the vitreous or sub-retinal area. When a patient is very high risk, the tumor presents itself with multiple features and is going to have to be treated with conservative treatment modalities or enucleation. International Classification for Intraocular Retinoblastoma Treatment. The priority of retinoblastoma treatment is to  preserve the life of the child, then to preserve vision, and then to minimize complications or side effects of treatment. The exact course of treatment depends on the individual case and is decided by the ophthalmologist in discussion with the paediatric oncologist. Correct treatment also depends on the mutation type, whether it is a germline RB1 mutation, a sporadic RB1 mutation or MYCN amplification with functional RB1. Children with involvement of both eyes at diagnosis usually require multimodality therapy (chemotherapy, local therapies). The various treatment modalities for retinoblastoma includes: Prognosis. In the developed world, retinoblastoma has one of the best  cure rates of all childhood cancers (95-98%), with more than 90% of sufferers surviving into adulthood. In the UK, around 40 to 50 new cases are diagnosed each year. Good prognosis depends upon early presentation of the child in health facility. Late presentation is associated with a poor prognosis. Survivors of hereditary retinoblastoma have a higher risk of developing other cancers later in life. Epidemiology. Retinoblastoma presents with cumulative lifetime incidence rate of one case of retinoblastoma per 18000 to 30000 live births worldwide. A higher incidence is noted in developing countries, which has been attributed to lower socioeconomic  status and the presence of human papilloma virus sequences in the retinoblastoma tissue. Almost 80% of children with retinoblastoma are diagnosed before three years of age and diagnosis in children above six years of age is extremely rare. In the UK, bilateral cases usually present within 14 to 16 months, while diagnosis of unilateral cases peaks between 24 and 30 months.