The effects of cancer on fertility:
- The ovarian cortex contains a limited number of follicles, which gradually decreases throughout a woman’s life as a result of ovulation and especially due to atresia. Radiotherapy and chemotherapy speed up the natural reduction of the number of follicles and prevent these from maturing. This, together with the fact that the ovaries cannot regenerate, can lead to premature ovarian failure.
- The number of primordial follicles which survive following exposure to chemotherapy depends on many different factors such as age, the type of cancer, the agent used (chemotherapy or radiotherapy), the dose and the number of cycles.
- Not everybody will lose their reproductive capacity, but continuing to menstruate is not synonymous with fertility. Although ovarian function may be recovered, the quality of oocytes may be suboptimal.
- For pregnant women who had cancer during their childhood, a higher rate of miscarriage has been observed, as well as a greater incidence of intrauterine growth retardation and of premature birth.
- Premature ovarian failure, in addition to putting an end to reproductive function, can also lead in the long term to vasomotor, skeletal and cardiovascular problems, as a result of the cessation of hormonal function.
There are currently several different options and treatments available to cancer patients for maintaining their fertility:
- Vitrification of ovocytes
- Freezing of the ovarian tissue
- Transposition of the ovaries
- Medical protection of the gonads (GnRH agonists): this could prevent follicles from reaching their sensitivity threshold to chemotherapy by suppressing granulosa cells. In tests done on rats treated with GnRH-a, inhibition of the recruitment process of small follicles from the reserve and their development into large follicles was demonstrated, which would subsequently proceed to development and atresia. The protective effect of GnRH-a may not be sufficient in the case of more prolonged treatments and higher doses of chemotherapy, in contrast to the shorter protocols used with animals.
Although its use is very controversial, the most recent randomised prospective studies seem to show it to be beneficial. However, its use should be restricted to controlled clinical trials. It has no applications for men..
- In vitro maturation of oocytes (IVM): this consists of recovering immature oocytes from small antral follicles which have not been stimulated or which have only been minimally stimulated, and their cultivation in a suitable medium until they reach maturity. In this way it is possible to avoid ovarian stimulation, and as a result it is a potential alternative to a standard IVF cycle. It may be useful in patients for whom, for one reason or another, it is in their interests to avoid ovarian stimulation, such as patients with hormone-dependent tumours.
Nowadays, IVM should be considered as a complementary technique to ovarian stimulation, useful in cases where there is no time to carry out ovarian stimulation, or when immature oocytes are obtained following stimulation, and as a complement to obtaining ovarian tissue.
These treatments targeting the preservation of fertility for cancer patients cannot guarantee that pregnancy will be achieved in the future, but they do mean that it will at least be possibly to try.