The potential implications of dysregulated DNA damage repair genes and their modulators as adjuvants for current chemotherapy regimens in Retinoblastoma tumors.

Retinoblastoma (RB) is the most common pediatric ocular malignancy resulting from biallelic inactivation of the RB1 gene and can be fatal if not treated. With advances in chemotherapy and earlier diagnosis, the mortality rates in developed nations such as USA, Europe and Canada, have reduced to 3-5 %. Subsequently, the clinical focus has shifted to preserving visual acuity in these countries, whereas in developing nations, mortality rates still range from 40 % to 70 %. In India, about 70 % of the children presenting with RB in the clinic have already progressed to category D or E tumors. Since chemotherapy is still a mainstay of RB treatment, bystander toxicity remains an important concern. Although enucleation is necessary in 40-60 % of the RB cases, prior chemotherapy is still administered in most cases to debulk the tumors. As the majority of drugs used in chemotherapy employ DNA damaging agents, the review attempts to summarize the current knowledge regarding dysregulated DNA damage repair (DDR) genes in RB. Loss of the RB1 gene causes not only unrestricted cell cycle progression and cell division, driven by the E2F transcription factor family, but also leads to the accumulation of various other mutations and chromosomal aberrations, which may have a specific impact on the patients' response to chemotherapy. Therefore, developing a more detailed perspective on the RB tumor DNA damage repair pathways is the focus of this review. Crystallizing the available information, we also propose the use of a few DDR inhibitors of the identified deregulated genes in retinoblastoma that are currently in clinical trials for other cancer types, as adjunct therapy to increase chemosensitivity of RB tumors and reduce chemotherapy-induced toxicity for better treatment outcomes.