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Retinoblastoma is the most common intraocular malignancy of infancy with an incidence of 1/15,000 to 1/20,000 births. Sixty percent of retinoblastomas are unilateral, with a median age at diagnosis of two years, and in most cases are not hereditary. Retinoblastoma is bilateral in 40% of cases, with an earlier median age at diagnosis of one year. All bilateral and multifocal unilateral forms are hereditary and are part of a genetic cancer predisposition syndrome. All children with a bilateral or familial form, and 10 to 15% of children with an unilateral form, constitutionally carry an RB1 gene mutation. The two most frequent symptoms revealing retinoblastoma are leukocoria and strabismus. Diagnosis is made by fundoscopy, with ultrasound and magnetic resonance imaging (MRI) contributing both to diagnosis and assessment of the extension of the disease. Treatment of patients with retinoblastoma must take into account the various aspects of the disease (unilateral/bilateral, size, localization…), the risk to vision and the possible hereditary nature of the disease. The main prognostic aspects are still premature detection and adapted coverage by a multi-disciplinary specialized team. Enucleation is still often necessary in unilateral disease; the decision for adjuvant treatment is taken according to the histological risk factors. The most important recent therapeutic advances concern the conservative treatment which is proposed for at least one of the two eyes in most bilateral cases: laser alone or in combination with chemotherapy, cryotherapy or brachytherapy. Recently, the development of new conservative techniques of treatment, such as intra-arterial selective chemotherapy perfusion, aims at preserving visual function in these children and decreasing the number of enucleations and the need for external beam radiotherapy. The vital prognosis related to retinoblatoma is now excellent in industrialized countries, but long-term survival is still related to the development of secondary tumors, mainly secondary sarcoma. Retinoblastoma requires multi-disciplinary care as well as a long term specialized follow-up. Early counseling of patients and their family concerning the risk of transmission of the disease and the risk of development of secondary tumors is necessary.

Children suffering with cancer have a higher probability of cure than adult. Since the 1950's, high cure rates have been achieved following remarkable progress in the overall care of these children. Not only children are more often "cured" than during the past century but they are probably "better cured" with the hope of experiencing less late effects. Nevertheless, there are still large disparities related to tumor diagnosis and regional area on the globe. If retinoblastoma is now cured in about 100% of the cases in industrialized countries, a different figure is seen unfortunately in economically disadvantaged countries. Not only is access to primary care lower, but also ophthalmologic techniques and available cancer treatments are less effective. Nowadays, such high cure rates observed for children with retinoblastoma are not the rule for all children with cancer. For example, despite considerable progress with new innovative treatments, the cure rate of children with metastatic neuroblastoma does not exceed 40%.

Metastatic relapse in children with solid tumors is mainly caused by systemic pretreatment dissemination of occult tumor cells. Therefore the initial detection of undetected metastases could have a clinical impact on the prognosis (i.e. new initial staging) and therapy for children with cancer. At later stage it is useful to determine the presence and change in the number of residual malignant cells in order to adjust and/or select adjuvant therapies and techniques (i.e. autologous bone marrow transplantation, leukapheresis.). Over the past decade, sensitive immunocytochemical and molecular assays have been developed which permit the identification of disseminated cancer cell. Actually tumor cell contamination can be detected in bone marrow or in peripheral blood of children with following cancers: neuroblastoma, Ewing tumor, alveolar rhabdomyosarcoma, PNETs. In this review, focus is on the recent technical achievements in the detection of occult cancer cells in bone marrow and in blood and a discussion of their usefulness for clinical trials.