Does fertility treatment increase the risk of uterine cancer? A meta-analysis

An ongoing debate over the last two decades has focused on whether fertility treatment in women may lead to an increased risk of developing uterine cancer over a period of time. Uterine cancer (including mainly endometrial carcinoma and the less common uterine sarcoma) is the commonest reproductive tract cancer and the fourth commonest cancer in women in the UK. Our objective was to assess the association between fertility drugs used in the treatment of female infertility (both as an independent therapy and during in vitro fertilization cycles) and the development of uterine cancer. A literature search was performed using Medline, Embase, Cochrane Library and Google Scholar databases for comparative studies until December 2014 to investigate a clinical significance of fertility treatment on the incidence of developing uterine cancer. General and MESH search headings, as well as the 'related articles' function were applied. All comparative studies of 'fertility treatment' versus 'non-fertility treatment' reporting the incidence of uterine cancer as an outcome were included. Uterine cancer incorporated the following terms: uterine cancer, uterine body tumours, uterine sarcomas and endometrial cancers. The primary outcome of interest was the uterine cancer incidence in all 'fertility treatment' versus 'non-fertility treatment' patient groups. Secondary outcomes of interest were: (a) uterine cancer incidence in 'IVF' versus 'non-IVF' patient groups; and (b) uterine cancer incidence according to type of fertility drug used. Odds ratio was the summary statistic. Random-effects modelling, graphical exploration and sensitivity analysis were used to evaluate the consistency of the calculated treatment effect. We included six studies in our final analysis, which comprised 776,224 patients in total. Of these, 103,758 had undergone fertility treatment and 672,466 had not. There was 100% agreement between the two reviewers regarding the data extraction. All the studies contained groups that were comparable in age, although the criteria of reporting age varied. Taking all studies into account, the incidence of uterine cancer was 0.14% (150 of 103,758) in the fertility treatment group and 2.22% (14,918 of 672,466) in the non-fertility treatment group. Using the random-effect model to analyze uterine cancer incidence, this difference was not found to be of statistical significance: OR 0.78 (95% CI, 0.39-1.57). The degree of heterogeneity was high (I(2)=68%). The risk for the development of uterine and in particular endometrial cancer posed by infertility and an unopposed oestrogen state is widely recognized. The present analysis aimed to perceive whether standard fertility drugs were also a risk to future uterine cancer development. The treatment does increase the concentrations of unopposed oestrogen for a short periods of time but if successful leads to fertility. This meta-analysis points to a non-deleterious effect of fertility drugs towards the development of uterine cancer, a conclusion strongly supported by our sub-group analysis.