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Retinoblastoma is a pediatric neoplasia with a high incidence in non-developed countries. Nowadays the diagnosis is clinical and unfortunately in advanced stages of the diseases, which puts the child´s life risk. The search for molecular diagnosis on retinoblastoma is necessary. Due to their location and tendency to migrate, biopsies of retinoblastoma are not recommended then, peripheral blood samples can be a good source for the search of biomarker. RT qPCR is a sensitive method for gene expression quantification; in order to achieve optimal results, a crucial step is the reference gene choice that cannot be neglected under any circumstance. Six of the most commonly used housekeeping genes; GAPDH, HPRT1, B2M, TBP, RPL13a and 18S, were tested in the blood samples of patients diagnosed with retinoblastoma and healthy controls.The HPRT and TBP were found the most reliable genes whereas GAPDH, that is one of the most commonly used genes for normalisation, together with B2M, RPL13a and 18S have to be avoided. Using the selected reference genes, the Rb mRNA showed significant differences between patients and healthy children whereas no differences were found using to control groups. In the present study, we validate blood samples of patients with retinoblastoma.

Loss of retinoblastoma (RB) function in the cone cells during retina development is necessary but not sufficient for retinoblastoma development. It has been reported that in the absence of RB activity, a retinoma is generated, and the onset of retina cancer occurs until the p53 pathway is altered. Unlike other types of cancer, in retinoblastoma the p53 tumour suppressor is mostly wild type, although its two primary regulators, MDMX and MDM2, are commonly dysregulated. A mutated RB form is inherited in around 35% of the cases, but normally two, somatic mutations are needed to alter the RB function. Here we investigated the mRNA levels of RB, p53, MDMX and MDM2 in peripheral blood samples of retinoblastoma patients to monitor the pathway status of p53 in somatic cells. We sought to investigate the involvement of these genes in the development of retina cancer, with the aim of identifying biomarkers for early diagnosis of this disease.

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