Advances in in vitro fertilization have generated crucial concerns about its long-term effects, particularly with regard to oncogenic risk in breast, uterus, and ovary. Recently, a study carried out by a team of Swedish researchers has reported that the probability of cancer/cancer therapy necessitating IVF, as a result of infertility, was much higher than the risk of developing cancer after IVF.
Bengt Kallen, Director, Tornblad Institute, University of Lund, Sweden, and coworkers, conducted the study to evaluate the rates of cancer risk in 24,058 Swedish women giving birth post-IVF, compared to rates in 1.39 million women in the general Swedish population between 1982 and 2006. The cancer registry included 1,279 post-IVF women and 95,775 women from the population. Information regarding births after the IVF treatment, and prolongation of the follow-up period of women undergoing therapy entailed the main objectives of the study, which was published in the journal, Human Reproduction. The study used Mantel-Haenszel odds ratio for the comparison, and considered and adjusted factors like smoking, parity, maternal age and year of delivery.
The study found that the cancer risk post-IVF was substantially lower (OR=0.74; 95% CI=0.67-0.82) when compared to pre-IVF (OR=1.37; 95% CI=1.27-1.48), owing primarily to a low breast and cervical cancer risk. The authors underlined that although the ovarian cancer risk showed an increase after IVF (2.13), it was still lesser than the risk before IVF (3.93). The findings were possibly a consequence of ovarian pathology raising the risk for both infertility and cancer, along with the decreased usage of oral contraceptives by infertile women, the authors surmised.
With the ongoing debate, assessments have compared cancer risk in post-IVF women and the general population. The comparison group in the current study composed of women who had a delivery during the observation period without any known IVF. This selection was done on the basis that pregnancy may have an impact on the oncogenic risk, possibly by a direct influence due to the pregnancy itself, or through the selection of the women. One such study by Mucci et al (Cancer Epidemiology, Biomarkers & Prevention, 2007) hypothesized that the long-term risk of getting ovarian cancer is associated with the hormonal disposition of a pregnancy. Another study by Cnattingius and colleagues (JAMA, 2005) suggests that the consequent maternal breast cancer risk is influenced by pregnancy hormones.
Kristiansson et al (Human Reproduction, 2007) reiterated that if there is any premenopausal cancer risk in women who give birth through IVF therapy, it is significantly low. This was in accordance with the findings that showed a low occurrence of carcinoma in situ (CIS) of the cervix and breast cancer. Similar inference was obtained in a study by Dor et al (Fertility Sterility, 2002) wherein cancer incidence rates in IVF-treated women were determined. The class of infertility, number of IVF cycles, and the therapy result did not notably affect the oncogenic risk potential.
Studies have attributed the development of cancer and its association with IVF to two probable correlations:
• Cancer and its treatment causing infertility and thereby requiring IVF
• Following IVF treatment, the therapy itself, including hormonal stimulation, will influence the risk of cancer
Although the current study had its limitations in terms of the patient selection and assessment, study group pertaining mostly to premenopausal women, and limited follow-up time, the results serve as valuable data for reassuring women on the lower risk of cancer associated with IVF. While further studies and long term analysis are warranted to validate the cancer risk potential in women who gave birth post IVF, the findings are both, speculative and indicative.
References
1. Källén B, Finnström O, Lindam A, Nilsson E, Nygren KG, Olausson PO. Malignancies among women who gave birth after in vitro fertilization. Hum Reprod. 2011 Jan;26(1):253-8.
2. Mucci LA, Dickman PW, Lambe M, et al. Gestational age and fetal growth in relation to maternal ovarian cancer risk in a Swedish cohort. Cancer Epidemiol Biomarkers Prev. 2007 Sep;16(9):1828-32.
3. Cnattingius S, Torrång A, Ekbom A, Granath F, Petersson G, Lambe M. Pregnancy characteristics and maternal risk of breast cancer. JAMA. 2005 Nov 16;294(19):2474-80.
4. Kristiansson P, Björ O, Wramsby H. Tumour incidence in Swedish women who gave birth following IVF treatment. Hum Reprod. 2007 Feb;22(2):421-6.
5. Dor J, Lerner-Geva L, Rabinovici J, et al. Cancer incidence in a cohort of infertile women who underwent in vitro fertilization. Fertil Steril. 2002 Feb;77(2):324-327.
