abstract/Cochrane Collaboration review: DNA-repair pathway inhibitors for the treatment of ovarian cancer (PARPs...AZD2281)

Plain language summary

Are DNA repair inhibitors as effective and harmless compared to conventional chemotherapy in the treatment of ovarian cancer?
Ovarian cancer is the sixth commonest cancer in women world-wide and remains a leading cause of death, with an annual incidence of 6.6 cases per 100,000 women and an annual mortality rate of 4.0 deaths per 100,000 women. Most ovarian cancers (90%) are epithelial ovarian cancer and arise from the surface of the ovary. Epithelial ovarian cancer typically occurs in post-menopausal women, with a peak incidence around the age of 60, although it does occur in younger women, often associated with genetic predispositions. The onset of this disease is insidious and 75% of women present with advanced stage disease (stage III or IV) when the 5 year survival is around 30%. Treatment consists of debulking surgery and platinum-based chemotherapy, with or without taxanes. Although initial response to chemotherapy is good, most women will relapse, requiring further chemotherapy treatment and develop cancer that is resistant to chemotherapy.

Conventinal chemotherapy acts on all rapidly dividing cells by damaging DNA. Cancer cells divide very rapidly, which is why chemotherapy works better on cancer cells than normal cells. However, there is no inherent selectivity for normal calls and so rapidly dividing cells, such as gut lining, hair follicles and bone marrow, are also affected, leading to diarrhoea, mouth ulcers, hair loss, anaemia and susceptibility to infections.

All cells are equipped with a number of systems or pathways that repair DNA damage. If cells are unable to repair their DNA, the cell undergoes programmed cell death (apoptosis) in order to prevent an abnormal cell from dividing. Because being able to repair DNA is vital to cell survival, normal cells have more than one DNA-repair pathway, so that if one is lost cells can still repair themselves. Cancer cells often develop defects in these pathways, due to mutations, which may promote development of cancer (e.g. BRCA mutations). However, these same mutations mean that these cancer cells are more susceptible to DNA damage, such as that caused by chemotherapy, than normal cells. Novel therapeutical agents have been developed to inhibit DNA-repair pathways, which makes cells that already have faults in another DNA repair pathway due to a mutation, exquisitely sensitive to DNA damaging chemotherapy agents. The most common target for this type of novel anti-cancer agent are the DNA-repair enzymes called poly (ADP-ribose) polymerases (PARPs). PARPs are a family of related enzymes, which are involved in regulating various cellular processes, including DNA repair, cell death, and inflammation. PARP inhibitors therefore have a potentially wide range of applications.

Our objective was to compare effectiveness and side effects of PARP inhibitors compared to conventional chemotherapy in women with ovarian cancer. The identification of a safe dose of AZD2281 (a PARP inhibitor) has been found by small non randomised trials, with encouraging results. For ovarian cancer, there are currently two ongoing RCTs, but outcome data are not yet available. Results of these trials are awaited to determine if DNA repair inhibitors have a role in addition to conventional chemotherapy in the treatment of ovarian cancer.

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COLLECTION AND ANALYSIS:
Two review authors independently assessed whether potentially relevant studies met the inclusion criteria. Searches for additional data and information were also performed by two independent review authors. No trials were found and therefore no data were analysed, so only information on excluded references was collected.
MAIN RESULTS: The search strategy identified 473 unique references of which 461 were excluded on the basis of title and abstract. The remaining 12 articles were retrieved in full, but none satisfied the inclusion criteria. However, two ongoing randomised phase II clinical trials were identified from the clinical trials databases that met our inclusion criteria, but no preliminary data were available.
AUTHORS' CONCLUSIONS: There are to date no published RCT data on the effectiveness and side effects of DNA-repair pathways inhibitors used alone or in association with conventional chemotherapy in the treatment of ovarian cancer. On-going trials have been identified and results are awaited and will be included in future updates of this review.