Cancer in Children: Clinical Management, 5th Edition

Chapter 25. Retinoblastoma

Guillermo L. Chantada

Enrique Schvartzman

Introduction

Retinoblastoma is a malignant endo-ocular tumour of children arising in the embryonic neural retina. It is the prototypical model for hereditary cancer development. Because of its rarity, most paediatricians and paediatric oncologists see few cases of this neoplasm, and diagnosis and management have traditionally been the reponsibility of ophthalmologists. In fact, ophthalmologists usually establish the diagnosis, decide the local treatment modalities, and monitor the response.

Although estimates vary, retinoblastoma occurs with a frequency of 1 in 15 000–18 000 live births in developed countries. However, it may be more frequent in less developed areas such as Latin America, Africa, and Asia. In such areas, retinoblastoma is diagnosed late when extraocular dissemination has already occurred, leading to higher morbidity (blindness) and mortality. There seems to be no predisposition for race or sex and no predilection for either eye.

Retinoblastoma can occur in two forms, heritable and non-heritable, and the tumours can be either unilateral or bilateral. All patients with bilateral retinoblastoma have the heritable disease, whereas only 10 per cent of unilateral cases have the heritable form. They tend to be younger and often have multifocal tumours. Non-heritable retinoblastoma is always unilateral and unifocal. Retinoblastoma can occur in a familial or sporadic form, but only 6–10 per cent are familial. The average age of patients at diagnosis is 24 months in unilateral cases and 13 months in bilateral cases.

Genetics

In 1971, Knudson developed a mathematical model to explain the heredity of retinoblastoma.¹ He suggested that ‘two hits’ should occur at a gene level to develop retinoblastoma. In heritable cases, a first event or ‘hit’ should be a germinal mutation, i.e. inherited and present in all cells of an affected individual. The second ‘hit’ occurs at some time during the development of the retinal cells, leading to retinoblastoma. In contrast, in non-heritable cases, both events occur in the retinal cells in an acquired fashion. According to this model, heritable retinoblastoma is inherited in an autosomal dominant fashion with approximately 95 per cent penetrance and high expressivity. However, some families show a different pattern characterized by reduced penetrance and expressivity. Some low-penetrance mutations have recently been characterized. Members of these families often develop only unilateral retinoblastoma or spontaneously regressing tumours called benign retinomas.

In 1985, the retinoblastoma gene (rb1) was isolated at chromosome 13q14. It is a large gene, spanning over 200 kb, and it is composed of 27 exons. This gene encodes a protein that plays a key role in the regulation of cell growth in normal cells acting at the checkpoint between G₁ and the entry to S phase. The phosphorylated form of the protein dissociates from the transcription factor E2F, freeing itself to promote progression to the cell cycle. In patients with retinoblastoma, functionally altered rb1 allows uncontrolled entry into the S phase leading to cell division. Sequences of the papillomavirus, which is known to interact with the rb1 pathway, have been found mostly in tumour tissue of unilateral patients with retinoblastoma from Mexico, suggesting that this virus may play a role in tumour development and possibly in the increased incidence in this area.²

Abnormalities at chromosome 13q14 can be detected by conventional karyotyping studies in only 5 per cent of cases. In the remainder, the mutations should be detected using more sophisticated molecular techniques. The mutations found in these cases vary from family to family, making molecular diagnosis very difficult and time-consuming since there are no sites with a high frequency of mutations within the retinoblastoma gene. Nonsense and frameshift mutations are the most frequent DNA alterations described.³ The first hit is usually a deletion or translocation at the rbl gene, occurring in either the maternal or paternal alelle; the second hit frequently involves the loss of heterozygosity of the remaining alelle, leading to neoplastic transformation.

Molecular diagnosis of retinoblastoma plays a key role in genetic counselling. If a germ-line mutation is identified in a given family, unaffected siblings can be tested and periodical fundoscopic examinations (under general anaesthesia in younger children) can be avoided in those who do not carry the abnormal gene. Prenatal diagnosis is also feasible, and when an abnormal retinoblastoma gene is detected in a fetus from an affected family, earlier delivery can be advised to treat the tumours as soon as possible. A useful card for genetic counselling developed by Abramson is shown in Figure 25.1.

Histology

Retinoblastoma is a tumour of neuroepithelial origin, which can be classified as one of the primitive neuroectodermal tumours of childhood. It consists of small undifferentiated anaplastic cells with scanty cytoplasm and large nuclei that stain deeply with haematoxylin, arising from the nucleated layer of the eye. Calcification occurs in necrotic areas and is a common feature of large tumours. Retinoblastoma cells often express antigens of photoreceptor differentiation and neuron-specific enolase but do not express CD99, glial fibrillary acidic protein, or S-100. Retinoblastoma cells express ganglioside GD2 almost invariably. Classically, two types of retinoblastoma have been described. The most common type is composed of highly undifferentiated retinoblasts; the other consists of more differentiated photoreceptor cells with neuroepithelial rosette formation. These Flexner–Wintersteiner rosettes are characteristic of retinoblastoma but they can be present in other ophthalmic tumours (medulloepithelioma). Less commonly seen in well-differentiated tumours is a ‘bouquet-like’ arrangement of benign-appearing cells with abundant cytoplasm, small nuclei, and long cytoplasmic processes traversing a fenestrated membrane. Depending on the level within the retina from which the retinoblastoma arises, the tumour may grow either in an endophytic pattern into the vitreous cavity or in an exophytic form into the subretinal space. Because of their friable nature, endophytic tumours can eventually seed the vitreous cavity and simulate a severe endophthalmitis. The active seeds of retinoblastoma can remain viable for long periods and eventually re-implant in the retina, giving rise to new tumours. In addition, seeding may occur following chemotherapy or radiation, since portions of the calcified mass break away and may contain viable tumour cells. When the tumour grows from the retina outwards into the subretinal space (exophytic pattern), it produces a retinal detachment, sometimes with no clear view of the mass, and can resemble Coats disease or other forms of exudative retinal detachment. Both patterns can occur in the same eye. Neither type is related to prognosis or responsiveness to treatment, but may affect the ease or difficulty in diagnosis evaluation. Another uncommon type of growth pattern, diffuse infiltrating retinoblastoma, is characterized by a flat infiltration of the retina by tumour cells and is usually found in older children. Retinoblastoma can disseminate outside the eye, following the course of the optic nerve and/or the subarachnoid space to the chiasm, the brain, and the meninges. It can also escape from the eyeball through the sclera and invade the orbit and beyond it to the surrounding structures. The tumour cells can also reach the choroid and, from there, they may gain access to the systemic circulation giving rise to haematogenous metastases. Metastatic retinoblastoma usually involves the central nervous system (CNS) either as a solitary mass or multiple lesions, or with leptomeningeal dissemination. It can also invade facial structures such as the pre-auricular lymph nodes and the bones of the skull. It can also give rise to haematogenous metastases involving the bone, bone marrow, and less frequently the liver, lungs, or any other organ.

Presenting signs and symptoms

The presenting signs and symptoms of retinoblastoma vary depending on where in the world a child with retinoblastoma is seen. In developing countries, proptosis and an orbital mass, sometimes with pre-auricular adenopathy indicating extraocular extension, are usually present at diagnosis (Fig. 25.2). In developed countries, parents seek medical care because of leukocoria (Fig. 25.3), strabismus, or, less frequently, for a red painful eye, glaucoma, or poor vision.⁴ Less common signs are rubeosis iridis (a reddish coloration of the iris), orbital cellulitis, heterochromia iridis (change in the colour of different parts of the iris), unilateral mydriasis, hyphaema (haemorrhage in the anterior chamber), or nystagmus. Leukocoria, a white reflex known as the cat's eye reflex, is the most common presenting sign of retinoblastoma. The whitish glow seen through the pupil is light momentarily reflected from the tumour. It is only seen when the child looks sideways or if the observer is at an oblique angle to the child's face as he or she looks straight ahead. It can also be noticed by parents or relatives in a flash photograph. Even though leukocoria is a quite specific sign with a narrow differential diagnosis, paediatricians often overlook it. Strabismus, the second most frequent presenting sign of retinoblastoma, is a non-specific sign which is present in many normal children, and is also often overlooked. Strabismus occurs when the tumour arises in the macular area, leading to an inability to fixate and subsequent deviation of the involved eye. Therefore a young child with strabismus calls for a dilated examination of the retina under anaesthesia with special attention given to the macula. When retinoblastoma is diagnosed in the first month of life, it is usually detected because of a positive family history.

Poor vision is seldom encountered because most children with retinoblastoma are too young to complain about visual impairment, but it may be the initial manifestation in older children. Another clinical manifestation, although less frequent, is a red painful eye, resembling orbital cellulitis. A syndrome associated with deletion of the long arm of chromosome 13 (the 13q-deletion syndrome) has been reported with the features of microcephaly, hypertelorism, micro-ophthalmos, epicanthal folds, micrognathia, short neck with lateral folds, low-set ears, imperforate anus, hypoplastic or absent thumbs, and psychomotor and mental retardation. Identification of these abnormalities may precede recognition of concomitant retinoblastoma. Such children require karyotype analysis and retinal examination. Another way in which the disease may be diagnosed early is by investigation in infants who have a family history of retinoblastoma.

Diagnosis

The most important step in diagnosis is examination of the eye under anaesthesia through fully dilated pupils, with indirect ophthalmoscopy and scleral indentation by an experienced ophthalmologist. Needle biopsies are not indicated for the diagnosis. Retinoblastoma is one of the few paediatric neoplasms that can be accurately diagnosed without histopathologic confirmation. Ultrasonography can be very helpful in the differential diagnosis of children with leukocoria. Two-dimensional B scan demonstrates the presence of a mass in the posterior segment in cases where the fundus may be obscured by detachment or haemorrhage, and shows a rounded or irregular intraocular mass with numerous highly reflective echoes in the orbit directly behind the tumour.

MRI is the method of choice for evaluating the optic nerve, orbital and CNS involvement, and the presence of an associated pinealoblastoma. This synchronous tumour, an entity that has been termed trilateral retinoblastoma, occurs in 2–3 per cent of bilateral heritable retinoblastoma cases, and it is not considered a metastasis but a separate primary tumour arising from cells of photoreceptor origin in the pineal gland and the suprasellar area. CTscans may be useful to detect intraocular calcifications but are not recommended routinely because they carry the risk of greater exposure to radiation. MRI also helps in differentiating retinoblastoma from Coats disease, a benign condition often confused with retinoblastoma. However, both MRI and CT scans are relatively unreliable for determining extension of the tumour into the sclera, choroid, or optic nerve, and invasion of these structures is only detected by histopathologic examination of the enucleated eye. Intraocular retinoblastoma should be differentiated from Coats disease, Toxocara infection, persistent hyperplastic primary vitreous, retrolental fibroplasias, and medulloepithelioma. Differential diagnoses of extraocular retinoblastoma include orbital rhabdomyosarcoma, metastatic neuroblastoma and leukaemia, and lymphoma. Bone marrow examination and biopsy and lumbar puncture for cytologic examination of the cerebrospinal fluid are mandatory when extraocular disease is suspected. Its yield is insignificant in patients with localized intraocular disease. In the presence of symptoms suggestive of metastatic disease (bone pain), a bone scan is indicated.

Follow-up

New tumours can develop up to the age of 7 years in patients with bilateral disease and so these children should be monitored regularly up to that age. Some bilateral cases present as unilateral disease, and tumours in the other eye may develop at follow-up examination up to 44 months of age. When new tumours develop in an eye with retinoblastoma, they seldom involve the macula.

Since tumours can appear in patients aged up to 28 months with a family history, a thorough ophthalmologic examination under anaesthesia should be performed shortly after birth and periodically up to that age in children born to affected parents.

Imaging studies are not routinely performed for the follow-up of patients with intraocular disease, but may be needed for monitoring patients with extraocular extension. The use of head MRI to screen for trilateral retinoblastoma during follow-up in young patients with hereditable retinoblastoma in order to facilitate earlier detection is under evaluation. There is no agreement on which imaging schedule (if any) can detect presymptomatic secondary malignancies in patients with heritable retinoblastoma.

Staging

The most widely used grouping system for retinoblastoma was proposed by Reese and Ellsworth (Table 25.1) and has become adopted as the standard for intraocular disease. Here, prognosis refers entirely to preservation of useful vision in the affected eye if radiation therapy is delivered via a lateral portal with photon therapy, and not to long-term survival. There is no widely accepted staging system for patients with extraocular disease.

Treatment

Two aspects of treatment of retinoblastoma must be considered: first, the local therapeutic options to treat intraocular disease and, secondly, systemic therapy for patients with extraocular, regional, or metastatic disease.

In developed countries, most patients present with intraocular disease and survival is 95 per cent. In these cases, treatment planning must consider the potential preservation of useful vision, minimizing the long-term sequelae. The size, number, and location of tumours and the status of the remaining eye are taken into account in choosing the best therapy. Even though an increasing number of patients with unilateral retinoblastoma can avoid enucleation in developed nations, eye preservation is uncommon in less privileged areas. Most patients with bilateral retinoblastoma come with advanced intraocular disease, often needing enucleation, in one eye and less advanced disease in the other eye, which can usually be preserved.

In developing countries, retinoblastoma is usually diagnosed after extraocular spread is evident. In these cases, the treatment of retinoblastoma aims to save the patient's life since death from metastatic disease is possible.

Surgery

Enucleation is the simplest and safest therapy for retinoblastoma. Resection of a long portion of optic nerve is mandatory. A prosthetic eyeball is fitted several weeks after the procedure to minimize the cosmetic effects. When enucleation is performed in the first 2 years of life, facial asymmetry develops because of inhibition of orbital growth.

Enucleation is indicated when no useful vision is predicted even if tumours are controlled. Most patients with Reese–Ellsworth stage V tumours require enucleation, especially when no useful vision can be achieved after successful treatment of the tumours. However, if the contralateral eye also has advanced disease, a conservative approach may be undertaken and a few eyes can be retained. Enucleation is mandatory when glaucoma, anterior chamber invasion, or rubeosis iridis are present and when local therapy cannot be evaluated because of a cataract or difficulty in following a patient closely.

Enucleation can be delayed when overt extrascleral extension is evident at diagnosis. Orbital masses usually shrink considerably after a few courses of chemotherapy, allowing enucleation to be performed and therefore avoiding orbital exenteration.⁵ There are few, if any, indications for orbital exenteration nowadays. Intraocular surgery, such as vitrectomy, is contraindicated in patients with proven or suspected retinoblastoma since it can increase the risk of orbital relapse.

External-beam radiotherapy

Retinoblastoma is a radiosensitive tumour and external-beam radiotherapy (EBRT) is the most effective local therapy for retinoblastoma. However, long-term side effects limit its use. EBRT is usually delivered using a linear accelerator to a dose of 40–45 Gy covering the whole retina. Infants must be anaesthetized and immobilized during the procedure, and close cooperation between the ophthalmologist and the radiotherapist is essential for planning the fields. Most radiotherapists use a D-shaped lateral field, which minimizes the risk of radiation-induced cataracts. Nevertheless, the anterior retina is underdosed with this technique, and recurrent tumours near the ora serrata are not uncommon.

The success rate of EBRT with this technique depends not only on tumour size, but also on location. Ophthalmoscopic regression patterns following radiotherapy have been characterized. Local control rates range from 58 to 80 per cent. Most recurrences after radiotherapy can be re-treated successfully with cryo- or photocoagulation. Long-term sequelae of radiotherapy are of great concern. Like enucleation, it causes inhibition of growth of the orbital bone, leading to cosmetic disturbances and, more importantly, it has been associated with an increased risk of secondary malignancies.

EBRT is also indicated for overt orbital disease and invasion of the cut end of the optic nerve. In these instances the chiasm should be included in the portal.

Plaque radiotherapy

Radioactive episcleral plaques using ⁶⁰Co, ¹⁰⁶Ru, or ¹²⁵I are used in the treatment of retinoblastoma. Plaques are inserted in the operating theatre by suturing them outside the sclera. They are removed in a second operation a few days later when the target dose has been administered. Plaque radiotherapy delivers an effective dose to the tumour while preserving the normal surrounding tissues from the adverse effects of radiotherapy. Plaques are usually prescribed for medium-size single tumours that are not amenable to cryo- or photocoagulation, but because of their high success rate, they have been increasingly used as primary therapy after chemoreduction. ¹²⁵I is the preferred isotope because of radiation safety for both patients and staff.

Cryo- and photocoagulation

Cryo- and photocoagulation are used to treat small (usually <5 mm) accessible tumours. They are widely available and can be repeated several times until local control is achieved. Cryotherapy is usually prescribed to treat anterior tumours and is applied with a small probe placed on the conjunctiva. Photocoagulation is generally used for posterior tumours, and is performed with either an argon laser or a xenon arc. However, photocoagulation should be avoided in tumours near the macula since it may leave a scar causing severe amblyopia. Both modalities cause little or no morbidity or long-term sequelae. The use of thermochemotherapy for posterior pole tumours has been recently described. It is based on the synergistic effect of intravenous carboplatin and hyperthermia administered by a diode laser.⁶

Chemotherapy

In the past, chemotherapy was only used to treat metastatic disease. However, in recent years, most groups have used chemotherapy as primary treatment for intraocular disease not amenable to local therapy in order to decrease tumour size and make the tumours suitable for local therapy.^7,8 This approach, called chemoreduction, may make it possible to avoid either enucleation or EBRT in selected cases. Carboplatin is the agent most frequently used since it has good penetration into theeye.Vincristine andetoposide arealso used; however, theirpenetration into the eye is unknown. Most intraocular tumours usually show dramatic shrinkage after systemic chemotherapy, but consolidation with local treatment appears to be needed in most cases to prevent relapse. Tumour location, patient age, and size of tumour all correlate with responsiveness to chemotherapy. Most patients with Reese–Ellsworth group I–IV tumours respond favourably to chemoreduction, so that enucleation and EBRT are usually avoided. Eye retention ranges from 74 to 100 per cent. Patients with Reese–Ellsworth group V disease, and especially those with vitreous seeds, have proved difficult to treat with this modality. After early encouraging results, it was reported that most require EBRT for effective tumour control and many are ultimately enucleated after chemotherapy and EBRT.⁸ Alternative treatment for these high-risk patients includes periocular administration of carboplatin or the association of intravenous cyclosporin with carboplatin in order to circumvent P-glycoprotein-mediated chemoresistance, which has been postulated by some groups as a potential cause of treatment failure.

Even though chemoreduction followed by local treatment has become an established therapy for intraocular retinoblastoma, there are several limitations to this approach. Long-term results and safety are unknown, especially as far as potential induction of secondary malignancies is concerned. The chemotherapy agents used are known to induce secondary leukaemia, especially the epipodophylotoxins used by many groups. The optimal regimen has not yet been determined, and the duration of treatment and the need for local therapy are also still under investigation.

Patients with unilateral disease are frequently best managed by enucleation. However, selected cases may benefit from chemoreduction and local therapy. Finally, treatment with chemoreduction and local treatment is tedious and needs meticulous management which is only available in specialized centers.

The role of adjuvant chemotherapy for patients with putative histopathologic risk factors for relapse is a matter of controversy. Post-enucleation histopathologic staging is essential to define groups with different risk of relapse.⁹ The paediatric oncologist faces the dilemma of prescribing adjuvant chemotherapy to all patients with putative risk factors, or of withholding it in controversial cases and treating those who relapse aggressively. Adjuvant chemotherapy does not completely eliminate the possibility of extraocular relapse, and its benefit in groups with low relapse rate is not proven. Because of the low relapse rate of this population, a randomized study comparing adjuvant treatment with observation would require an enormous number of patients. Many authors consider extraocular relapse as a catastrophic event and recommend adjuvant therapy for all patients with histopathologic risk factors.¹⁰ However, in recent years it has been shown that many relapsed patients can be salvaged by intensive therapy.^5,11 Therefore avoiding adjuvant chemotherapy for patients with a low probability of relapse and treating those who relapse aggressively is a reasonable alternative.¹²

There is almost universal agreement that there is no need for adjuvant chemotherapy for patients with intraretinal disease and those with pre-laminar optic nerve invasion.^9,12 The role of chemotherapy in isolated choroidal invasion is controversial. It has been suggested that once the tumour invades the choroid, it may gain access to the systemic circulation, giving rise to haematogenous metastasis and thus justifying adjuvant therapy.¹⁰ However, in our series of 55 patients with isolated choroidal invasion treated only with enucleation, only one had an extraocular relapse.¹² Therefore, according to our data, chemotherapy is not needed in this population. Choroidal invasion may only be relevant when it is combined with post-laminar optic nerve invasion.

Invasion of the optic nerve beyond the lamina cribrosa is a major risk factor for relapse, especially when the cut end is involved. When the cut end is free from tumour, management is controversial. At our center, patients with this condition receive no therapy other than enucleation provided that there is no major choroidal or scleral invasion. In our published series of 21 patients treated with enucleation and no adjuvant therapy, none relapsed.¹² Patients with concomitant major choroidal involvement with or without scleral invasion have a greater risk of relapse, and adjuvant chemotherapy is indicated. Patients with invasion of the cut end of the optic nerve are uniformly considered as having a high risk of relapse. Survival rate has been reported to be as low as 40 per cent. However, with multimodal treatment, including adjuvant chemotherapy and orbital radiotherapy involving the optic chiasm, 11/14 patients survived at our institution.⁹ The role of intrathecal chemotherapy in these situations remains to be established. According to our limited experience, patients with microscopic scleral involvement are at high risk for extraocular relapse and should receive adjuvant therapy.⁹

When overt extraocular disease is present, pre-enucleation chemotherapy is warranted.⁵ Doz et al. ¹³ pioneered the use of the combination of carboplatin and etoposide, which became the gold standard. A phase II study showed an overall 60 per cent response rate of extraocular retinoblastoma to idarubicin, which may be the anthracycline of choice.¹⁴ Response to other agents has been studied in single patients or small series. Cisplatin, cyclophosphamide, ifosfamide, vincristine, doxorubicin, topotecan, and thiotepa are frequently used. With a multimodal approach combining chemotherapy, limited surgery, and radiotherapy to the involved areas, a 5-year probability of event-free survival of 84 per cent for patients with overt orbital disease with or without pre-auricular node invasion as their only metastatic site was achieved.⁵ However, even though complete remission is usually achieved with conventional chemotherapy in patients with metastatic disease (haematogenous or CNS), it is usually shortlived and ultimate survival is infrequent.^5,9 High-dose chemotherapy followed by autologous stem cell rescue has proven efficacy for the treatment of patients with systemic relapse, but it is of less value in cases of CNS dissemination.¹¹ Conditioning regimens have usually included the drugs mentioned above at higher dose. There is no effective therapy for these patients, and most centers treat them according to investigational protocols or palliatively. They may need craniospinal radiation to achieve disease control, but the high frequency of neuropsychologic sequelae in young children precludes its use.

The drug combination used for extraocular disease at our center⁵ is shown in Table 25.2.

Secondary malignancies

The presence of a germ-line mutation at the retinoblastoma gene confers on affected individuals a lifetime high predisposition for secondary malignancies. Conversely, unilateral retinoblastoma patients without the constitutional mutation are at no risk for developing second tumours. With current therapy, there are more patients with bilateral retinoblastoma dying of secondary malignancies than those who succumb from the retinoblastoma itself. The risk of developing a secondary malignancy exists among these children regardless of the therapy received. However, those patients receiving radiotherapy in the first year of life appear to be at greater risk.¹⁵

The cumulative risk of second cancers is 1 per cent per year, reaching 51 per cent 50 years after the diagnosis of retinoblastoma. The median latency period is 15 years. Those who survive a secondary malignancy are at increased risk of developing additional malignancies at a rate of about 2 per cent per year.

Most secondary cancers seen in patients with bilateral retinoblastoma are sarcomas, usually osteosarcomas of the irradiated orbit. Sarcomas outside the orbit, cutaneous melanoma, thyroid carcinoma, and lung and breast cancer have also been reported. The risk for osteogenic sarcoma is greater at age 10–20 years and brain tumours tend to present later. Secondary malignancies in these patients are usually very aggressive and are frequently fatal. However, they should be treated with curative intent. A high index of suspicion and aggressive treatment have improved results in recent years.

References

1. Knudson AG (1971). Mutation and cancer: statistical study of retinoblastoma. Proc Natl Acad Sci USA 68, 820–3.

2. Orjuela M, Ponce Castaneda V, Ridaura C, et al. (2000). Presence of human papilloma virus in tumor tissue from children with retinoblastoma: an alternative mechanism for tumor development. Clin Cancer Res 6, 4010–16.

3. Harbour W (1998). Overview of RB gene mutations in patients with retinoblastoma. Implications for genetic screening. Ophthalmology 105, 1442–7.

4. Abramson DH, Frank C, Susman M, Whalen M, Dunkel I, Boyd N (1998). Presenting signs of retinoblastoma. J Pediatr 132, 505–8.

5. Chantada G, Fandi[not tilde]o A, Casak S, et al. (2003). Treatment of overt extraocular retinoblastoma. Med Pediatr Oncol 40, 158–61.

6. Lumbroso L, Doz F, Urbieta M, et al. (2002). Chemothermotherapy in the management of retinoblastoma. Ophthalmology 109, 1130–6.

7. Kingston J, Hungerford J, Madreperla S, Plowman P (1996). Results of combined chemotherapy and radiotherapy for advanced intraocular retinoblastoma. Arch Ophthalmol 114, 1339–43.

8. Shields C, Honavar S, Meadows A, et al. (2002). Chemoreduction plus focal therapy for retinoblastoma: factors predictive of need for treatment with external beam radiotherapy or enucleation. Am J Ophthalmol 133, 657–64.

9. Schvartzman E, Chantada G, Fandi[not tilde]oA, et al. (1996). Results of a stage-based protocol for the treatment of retinoblastoma. J Clin Oncol 14, 1532–6.

10. Honavar G, Singh A, Shields C, et al. (2002). Post enucleation adjuvant therapy in high risk retinoblastoma. Arch Ophthalmol 120, 923–31.

11. Dunkel IJ, Aledo A, Kernan NA, et al. (2000). Successful treatment of metastatic retinoblastoma. Cancer 89, 2117–21.

12. Chantada GL, Dunkel IJ, de Dávila MT, Abramson DH (2004). Retinoblastoma patients with high risk ocular pathological features: Who needs adjuvant therapy? Br. J. Ophthalmol 88, 1069–73.

13. Doz F, Neuenshwander S, Plantaz D, et al. (1995). Etoposide and carboplatin in extraocular retinoblastoma: a study by the Societé Franc¸aise d'Oncologie Pédiatrique. J Clin Oncol 13, 902–9.

14. Chantada GL, Fandi[not tilde]o A, Mato G, et al. (1999). A phase II window of idarubicin in children with extraocular retinoblastoma. J Clin Oncol 17, 1847–50.

15. Moll A, Imhof S, Schouten van Meeteren AY, et al. (2001). Second primary tumors in hereditary retinoblastoma: a register-based study, 1945–1997. Ophthalmology 108, 1109–14.